diff --git a/app/controllers/api/cart_controller.rb b/app/controllers/api/cart_controller.rb
index 829bd29bb..4a6b40e6a 100644
--- a/app/controllers/api/cart_controller.rb
+++ b/app/controllers/api/cart_controller.rb
@@ -1,6 +1,6 @@
 # frozen_string_literal: true
 
-# API Controller for manage user's cart
+# API Controller to manage user's cart
 class API::CartController < API::ApiController
   include API::OrderConcern
 
@@ -13,6 +13,17 @@ class API::CartController < API::ApiController
     render 'api/orders/show'
   end
 
+  def create_item
+    authorize @current_order, policy_class: CartPolicy
+    service = Cart::CreateCartItemService.new(@current_order)
+    @item = service.create(params)
+    if @item.save({ context: @current_order.order_items })
+      render 'api/orders/item', status: :created
+    else
+      render json: @item.errors.full_messages, status: :unprocessable_entity
+    end
+  end
+
   def add_item
     authorize @current_order, policy_class: CartPolicy
     @order = Cart::AddItemService.new.call(@current_order, orderable, cart_params[:quantity])
diff --git a/app/models/cart_item/machine_reservation.rb b/app/models/cart_item/machine_reservation.rb
index b85d71e15..790244d8a 100644
--- a/app/models/cart_item/machine_reservation.rb
+++ b/app/models/cart_item/machine_reservation.rb
@@ -19,7 +19,7 @@ class CartItem::MachineReservation < CartItem::Reservation
     'machine'
   end
 
-  def valid?(all_items)
+  def valid?(all_items = [])
     cart_item_reservation_slots.each do |slot|
       same_hour_slots = SlotsReservation.joins(:reservation).where(
         reservations: { reservable: reservable },
diff --git a/app/models/cart_item/prepaid_pack.rb b/app/models/cart_item/prepaid_pack.rb
index 8e1053435..73333f536 100644
--- a/app/models/cart_item/prepaid_pack.rb
+++ b/app/models/cart_item/prepaid_pack.rb
@@ -3,6 +3,7 @@
 # A prepaid-pack added to the shopping cart
 class CartItem::PrepaidPack < CartItem::BaseItem
   belongs_to :prepaid_pack
+  belongs_to :customer_profile, class_name: 'InvoicingProfile'
 
   def customer
     customer_profile.user
@@ -36,11 +37,11 @@ class CartItem::PrepaidPack < CartItem::BaseItem
 
   def valid?(_all_items)
     if pack.disabled
-      @errors[:item] = I18n.t('cart_item_validation.pack')
+      errors.add(:prepaid_pack, I18n.t('cart_item_validation.pack'))
       return false
     end
     if pack.group_id != customer.group_id
-      @errors[:group] = "pack is reserved for members of group #{pack.group.name}"
+      errors.add(:group, "pack is reserved for members of group #{pack.group.name}")
       return false
     end
     true
diff --git a/app/models/cart_item/reservation.rb b/app/models/cart_item/reservation.rb
index 7e792a1ee..68ad770a0 100644
--- a/app/models/cart_item/reservation.rb
+++ b/app/models/cart_item/reservation.rb
@@ -52,7 +52,7 @@ class CartItem::Reservation < CartItem::BaseItem
     reservable&.name
   end
 
-  def valid?(all_items)
+  def valid?(all_items = [])
     pending_subscription = all_items.find { |i| i.is_a?(CartItem::Subscription) }
 
     reservation_deadline_minutes = Setting.get('reservation_deadline').to_i
diff --git a/app/policies/cart_policy.rb b/app/policies/cart_policy.rb
index b63dcbcac..db442a808 100644
--- a/app/policies/cart_policy.rb
+++ b/app/policies/cart_policy.rb
@@ -6,7 +6,7 @@ class CartPolicy < ApplicationPolicy
     !Setting.get('store_hidden') || user&.privileged?
   end
 
-  %w[add_item remove_item set_quantity refresh_item validate].each do |action|
+  %w[add_item remove_item set_quantity refresh_item validate create_item].each do |action|
     define_method "#{action}?" do
       return user.privileged? || (record.statistic_profile_id == user.statistic_profile.id) if user
 
diff --git a/app/services/cart/add_item_service.rb b/app/services/cart/add_item_service.rb
index 6f868d0fd..952cc7b02 100644
--- a/app/services/cart/add_item_service.rb
+++ b/app/services/cart/add_item_service.rb
@@ -8,8 +8,8 @@ class Cart::AddItemService
     item = case orderable
            when Product
              add_product(order, orderable, quantity)
-           when Slot
-             add_slot(order, orderable)
+           when /^CartItem::/
+             add_cart_item(order, orderable)
            else
              raise Cart::UnknownItemError
            end
@@ -42,11 +42,7 @@ class Cart::AddItemService
     item
   end
 
-  def add_slot(order, orderable)
-    item = order.order_items.find_by(orderable: orderable)
-
-    item = order.order_items.new(quantity: 1, orderable: orderable, amount: orderable.amount || 0) if item.nil?
-
-    item
+  def add_cart_item(order, orderable)
+    order.order_items.new(quantity: 1, orderable: orderable, amount: orderable.price.amount || 0)
   end
 end
diff --git a/app/services/cart/create_cart_item_service.rb b/app/services/cart/create_cart_item_service.rb
new file mode 100644
index 000000000..2c59b50d0
--- /dev/null
+++ b/app/services/cart/create_cart_item_service.rb
@@ -0,0 +1,110 @@
+# frozen_string_literal: true
+
+# Provides methods to create new cart items, based on an existing Order
+class Cart::CreateCartItemService
+  def initialize(order)
+    @order = order
+    @customer = order.user
+    @operator = order.user.privileged? ? order.operator_profile.user : order.user
+  end
+
+  def create(item)
+    key = item.keys.filter { |k| %w[subscription reservation prepaid_pack free_extension].include?(k) }.first
+    case key
+    when 'subscription', :subscription
+      subscription = create_subscription(item.require(:subscription).permit!)
+      update_reservations(subscription)
+      subscription
+    when 'reservation', :reservation
+      create_reservation(item.require(:reservation).permit!)
+    when 'prepaid_pack', :prepaid_pack
+      create_prepaid_pack(item.require(:prepaid_pack).permit!)
+    when 'free_extension', :free_extension
+      create_free_extension(item.require(:free_extension).permit!)
+    else
+      raise NotImplementedError, "unknown item type #{item.keys.first}"
+    end
+  end
+
+  private
+
+  def create_subscription(cart_item)
+    CartItem::Subscription.new(
+      plan: Plan.find(cart_item[:plan_id]),
+      customer_profile: @customer.invoicing_profile,
+      start_at: cart_item[:start_at]
+    )
+  end
+
+  def update_reservations(new_subscription)
+    @order.order_items
+          .where(orderable_type: %w[CartItem::MachineReservation CartItem::SpaceReservation CartItem::TrainingReservation])
+          .find_each do |reserv|
+      reserv.update(plan: new_subscription.plan, new_subscription: true)
+    end
+  end
+
+  def create_reservation(cart_item)
+    plan_info = subscription_info
+    reservable = cart_item[:reservable_type]&.constantize&.find(cart_item[:reservable_id])
+    case reservable
+    when Machine
+      CartItem::MachineReservation.new(customer_profile: @customer.invoicing_profile,
+                                       operator_profile: @operator.invoicing_profile,
+                                       reservable: reservable,
+                                       cart_item_reservation_slots_attributes: cart_item[:slots_reservations_attributes],
+                                       plan: plan_info[:subscription]&.plan,
+                                       new_subscription: plan_info[:new_subscription])
+    when Training
+      CartItem::TrainingReservation.new(customer_profile: @customer.invoicing_profile,
+                                        operator_profile: @operator.invoicing_profile,
+                                        reservable: reservable,
+                                        cart_item_reservation_slots_attributes: cart_item[:slots_reservations_attributes],
+                                        plan: plan_info[:subscription]&.plan,
+                                        new_subscription: plan_info[:new_subscription])
+    when Event
+      CartItem::EventReservation.new(customer_profile: @customer.invoicing_profile,
+                                     operator_profile: @operator.invoicing_profile,
+                                     event: reservable,
+                                     cart_item_reservation_slots_attributes: cart_item[:slots_reservations_attributes],
+                                     normal_tickets: cart_item[:nb_reserve_places],
+                                     cart_item_event_reservation_tickets_attributes: cart_item[:tickets_attributes] || {})
+    when Space
+      CartItem::SpaceReservation.new(customer_profile: @customer.invoicing_profile,
+                                     operator_profile: @operator.invoicing_profile,
+                                     reservable: reservable,
+                                     cart_item_reservation_slots_attributes: cart_item[:slots_reservations_attributes],
+                                     plan: plan_info[:subscription]&.plan,
+                                     new_subscription: plan_info[:new_subscription])
+    else
+      raise NotImplementedError, "unknown reservable type #{reservable}"
+    end
+  end
+
+  def create_prepaid_pack(cart_item)
+    CartItem::PrepaidPack.new(
+      prepaid_pack: PrepaidPack.find(cart_item[:id]),
+      customer_profile: @customer.invoicing_profile
+    )
+  end
+
+  def create_free_extension(cart_item)
+    plan_info = subscription_info
+    CartItem::FreeExtension.new(
+      customer_profile: @customer.invoicing_profile,
+      subscription: plan_info[:subscription],
+      new_expiration_date: cart_item[:end_at]
+    )
+  end
+
+  def subscription_info
+    cart_subscription = @order.order_items.find_by(orderable_type: 'CartItem::Subscription')
+    if cart_subscription
+      { subscription: cart_subscription, new_subscription: true }
+    elsif @customer.subscribed_plan
+      { subscription: @customer.subscription, new_subscription: false } unless @customer.subscription.expired_at < DateTime.current
+    else
+      { subscription: nil, new_subscription: false }
+    end
+  end
+end
diff --git a/app/views/api/orders/item.json.jbuilder b/app/views/api/orders/item.json.jbuilder
new file mode 100644
index 000000000..7c3963b94
--- /dev/null
+++ b/app/views/api/orders/item.json.jbuilder
@@ -0,0 +1,4 @@
+# frozen_string_literal: true
+
+json.id @item.id
+json.type @item.class.name
diff --git a/config/routes.rb b/config/routes.rb
index 31823d03f..2f620d93b 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -168,6 +168,7 @@ Rails.application.routes.draw do
       put 'set_offer', on: :collection
       put 'refresh_item', on: :collection
       post 'validate', on: :collection
+      post 'create_item', on: :collection
     end
     resources :checkout, only: %i[] do
       post 'payment', on: :collection
diff --git a/db/schema.rb b/db/schema.rb
index 4ed4819f2..4ba30590d 100644
--- a/db/schema.rb
+++ b/db/schema.rb
@@ -19,8 +19,8 @@ ActiveRecord::Schema.define(version: 2023_01_31_104958) do
   enable_extension "unaccent"
 
   create_table "abuses", id: :serial, force: :cascade do |t|
-    t.string "signaled_type"
     t.integer "signaled_id"
+    t.string "signaled_type"
     t.string "first_name"
     t.string "last_name"
     t.string "email"
@@ -68,8 +68,8 @@ ActiveRecord::Schema.define(version: 2023_01_31_104958) do
     t.string "locality"
     t.string "country"
     t.string "postal_code"
-    t.string "placeable_type"
     t.integer "placeable_id"
+    t.string "placeable_type"
     t.datetime "created_at"
     t.datetime "updated_at"
   end
@@ -93,8 +93,8 @@ ActiveRecord::Schema.define(version: 2023_01_31_104958) do
   end
 
   create_table "assets", id: :serial, force: :cascade do |t|
-    t.string "viewable_type"
     t.integer "viewable_id"
+    t.string "viewable_type"
     t.string "attachment"
     t.string "type"
     t.datetime "created_at"
@@ -281,8 +281,8 @@ ActiveRecord::Schema.define(version: 2023_01_31_104958) do
   end
 
   create_table "credits", id: :serial, force: :cascade do |t|
-    t.string "creditable_type"
     t.integer "creditable_id"
+    t.string "creditable_type"
     t.integer "plan_id"
     t.integer "hours"
     t.datetime "created_at"
@@ -524,15 +524,15 @@ ActiveRecord::Schema.define(version: 2023_01_31_104958) do
 
   create_table "notifications", id: :serial, force: :cascade do |t|
     t.integer "receiver_id"
-    t.string "attached_object_type"
     t.integer "attached_object_id"
+    t.string "attached_object_type"
     t.integer "notification_type_id"
     t.boolean "is_read", default: false
     t.datetime "created_at"
     t.datetime "updated_at"
     t.string "receiver_type"
     t.boolean "is_send", default: false
-    t.jsonb "meta_data", default: "{}"
+    t.jsonb "meta_data", default: {}
     t.index ["notification_type_id"], name: "index_notifications_on_notification_type_id"
     t.index ["receiver_id"], name: "index_notifications_on_receiver_id"
   end
@@ -772,8 +772,8 @@ ActiveRecord::Schema.define(version: 2023_01_31_104958) do
   create_table "prices", id: :serial, force: :cascade do |t|
     t.integer "group_id"
     t.integer "plan_id"
-    t.string "priceable_type"
     t.integer "priceable_id"
+    t.string "priceable_type"
     t.integer "amount"
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
@@ -976,8 +976,8 @@ ActiveRecord::Schema.define(version: 2023_01_31_104958) do
     t.text "message"
     t.datetime "created_at"
     t.datetime "updated_at"
-    t.string "reservable_type"
     t.integer "reservable_id"
+    t.string "reservable_type"
     t.integer "nb_reserve_places"
     t.integer "statistic_profile_id"
     t.index ["reservable_type", "reservable_id"], name: "index_reservations_on_reservable_type_and_reservable_id"
@@ -986,8 +986,8 @@ ActiveRecord::Schema.define(version: 2023_01_31_104958) do
 
   create_table "roles", id: :serial, force: :cascade do |t|
     t.string "name"
-    t.string "resource_type"
     t.integer "resource_id"
+    t.string "resource_type"
     t.datetime "created_at"
     t.datetime "updated_at"
     t.index ["name", "resource_type", "resource_id"], name: "index_roles_on_name_and_resource_type_and_resource_id"
diff --git a/test/integration/order/create_cart_item_test.rb b/test/integration/order/create_cart_item_test.rb
new file mode 100644
index 000000000..7fba81874
--- /dev/null
+++ b/test/integration/order/create_cart_item_test.rb
@@ -0,0 +1,165 @@
+# frozen_string_literal: true
+
+require 'test_helper'
+
+class CreateCartItemTest < ActionDispatch::IntegrationTest
+  setup do
+    @user = User.find_by(username: 'pdurand')
+    login_as(@user, scope: :user)
+    @order = Cart::FindOrCreateService.new(@user).call(nil)
+  end
+
+  test 'create a subscription' do
+    plan = Plan.first
+    post '/api/cart/create_item',
+         params: {
+           order_token: @order.token,
+           subscription: {
+             plan_id: plan.id
+           }
+         }
+    # general assertions
+    assert_equal 201, response.status
+    assert_equal Mime[:json], response.content_type
+
+    # Check the cart item was created correctly
+    res = json_response(response.body)
+    resource = res[:type].classify.constantize.find(res[:id])
+    assert resource.is_a? CartItem::Subscription
+    assert_equal plan, resource.plan
+  end
+
+  test 'create a machine reservation' do
+    machine = Machine.first
+    post '/api/cart/create_item',
+         params: {
+           order_token: @order.token,
+           reservation: {
+             reservable_id: machine.id,
+             reservable_type: 'Machine',
+             slots_reservations_attributes: [
+               { slot_id: machine.availabilities.last&.slots&.last&.id }
+             ]
+           }
+         }
+    # general assertions
+    assert_equal 201, response.status
+    assert_equal Mime[:json], response.content_type
+
+    # Check the cart item was created correctly
+    res = json_response(response.body)
+    resource = res[:type].classify.constantize.find(res[:id])
+    assert resource.is_a? CartItem::MachineReservation
+    assert_equal machine, resource.reservable
+  end
+
+  test 'create a space reservation' do
+    space = Space.first
+    post '/api/cart/create_item',
+         params: {
+           order_token: @order.token,
+           reservation: {
+             reservable_id: space.id,
+             reservable_type: 'Space',
+             slots_reservations_attributes: [
+               { slot_id: space.availabilities.last&.slots&.last&.id }
+             ]
+           }
+         }
+    # general assertions
+    assert_equal 201, response.status
+    assert_equal Mime[:json], response.content_type
+
+    # Check the cart item was created correctly
+    res = json_response(response.body)
+    resource = res[:type].classify.constantize.find(res[:id])
+    assert resource.is_a? CartItem::SpaceReservation
+    assert_equal space, resource.reservable
+  end
+
+  test 'create a training reservation' do
+    training = Training.first
+    post '/api/cart/create_item',
+         params: {
+           order_token: @order.token,
+           reservation: {
+             reservable_id: training.id,
+             reservable_type: 'Training',
+             slots_reservations_attributes: [
+               { slot_id: training.availabilities.last&.slots&.last&.id }
+             ]
+           }
+         }
+    # general assertions
+    assert_equal 201, response.status
+    assert_equal Mime[:json], response.content_type
+
+    # Check the cart item was created correctly
+    res = json_response(response.body)
+    resource = res[:type].classify.constantize.find(res[:id])
+    assert resource.is_a? CartItem::TrainingReservation
+    assert_equal training, resource.reservable
+  end
+
+  test 'create an event reservation' do
+    event = Event.find(4)
+    post '/api/cart/create_item',
+         params: {
+           order_token: @order.token,
+           reservation: {
+             reservable_id: event.id,
+             reservable_type: 'Event',
+             slots_reservations_attributes: [
+               { slot_id: event.availability.slots.last&.id }
+             ],
+             nb_reserve_places: 2
+           }
+         }
+    # general assertions
+    assert_equal 201, response.status
+    assert_equal Mime[:json], response.content_type
+
+    # Check the cart item was created correctly
+    res = json_response(response.body)
+    resource = res[:type].classify.constantize.find(res[:id])
+    assert resource.is_a? CartItem::EventReservation
+    assert_equal event, resource.event
+    assert_equal 2, resource.normal_tickets
+  end
+
+  test 'create a prepaid-pack' do
+    pack = PrepaidPack.first
+    post '/api/cart/create_item',
+         params: {
+           order_token: @order.token,
+           prepaid_pack: { id: pack.id }
+         }
+    # general assertions
+    assert_equal 201, response.status
+    assert_equal Mime[:json], response.content_type
+
+    # Check the cart item was created correctly
+    res = json_response(response.body)
+    resource = res[:type].classify.constantize.find(res[:id])
+    assert resource.is_a? CartItem::PrepaidPack
+    assert_equal pack.id, resource.prepaid_pack_id
+  end
+
+  test 'create a free-extension for a subscription' do
+    subscription = @user.subscription
+    post '/api/cart/create_item',
+         params: {
+           order_token: @order.token,
+           free_extension: { end_at: subscription.expiration_date + 1.month }
+         }
+    # general assertions
+    assert_equal 201, response.status
+    assert_equal Mime[:json], response.content_type
+
+    # Check the cart item was created correctly
+    res = json_response(response.body)
+    resource = res[:type].classify.constantize.find(res[:id])
+    assert resource.is_a? CartItem::FreeExtension
+    assert_equal subscription.id, resource.subscription_id
+  end
+end