diff --git a/CHANGELOG.md b/CHANGELOG.md
index e63f44cb4..e883489b3 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
 # Changelog Fab-manager
 
 - Fix a bug: unable to export members list if no subscriptions was taken
+- Fix a bug: most OpenAPI endpoints were dysfunctional
 
 ## v5.0.6 2021 June 21
 
diff --git a/app/controllers/open_api/v1/base_controller.rb b/app/controllers/open_api/v1/base_controller.rb
index 45cce71f8..3d96c8d8b 100644
--- a/app/controllers/open_api/v1/base_controller.rb
+++ b/app/controllers/open_api/v1/base_controller.rb
@@ -1,5 +1,8 @@
 # frozen_string_literal: true
 
+# module definition
+module OpenAPI::V1; end
+
 # Parameters for OpenAPI endpoints
 class OpenAPI::V1::BaseController < ActionController::Base
   protect_from_forgery with: :null_session
diff --git a/app/controllers/open_api/v1/bookable_machines_controller.rb b/app/controllers/open_api/v1/bookable_machines_controller.rb
index d7a981d76..efbd40cae 100644
--- a/app/controllers/open_api/v1/bookable_machines_controller.rb
+++ b/app/controllers/open_api/v1/bookable_machines_controller.rb
@@ -1,3 +1,6 @@
+# frozen_string_literal: true
+
+# authorized 3rd party softwares can list the bookable machines through the OpenAPI
 class OpenAPI::V1::BookableMachinesController < OpenAPI::V1::BaseController
   extend OpenAPI::ApiDoc
   expose_doc
@@ -22,19 +25,15 @@ class OpenAPI::V1::BookableMachinesController < OpenAPI::V1::BaseController
 
 
 
-    if user.subscription
-      plan_id = user.subscription.plan_id
+    return unless user.subscription
 
-      @machines.each do |machine|
-        credit = Credit.find_by(plan_id: plan_id, creditable: machine)
-        users_credit = user.users_credits.find_by(credit: credit) if credit
+    plan_id = user.subscription.plan_id
 
-        if credit
-          @hours_remaining[machine.id] = credit.hours - (users_credit.try(:hours_used) || 0)
-        else
-          @hours_remaining[machine.id] = 0
-        end
-      end
+    @machines.each do |machine|
+      credit = Credit.find_by(plan_id: plan_id, creditable: machine)
+      users_credit = user.users_credits.find_by(credit: credit) if credit
+
+      @hours_remaining[machine.id] = credit ? credit.hours - (users_credit.try(:hours_used) || 0) : 0
     end
   end
 end
diff --git a/app/controllers/open_api/v1/events_controller.rb b/app/controllers/open_api/v1/events_controller.rb
index 169c367ef..920bf6ce8 100644
--- a/app/controllers/open_api/v1/events_controller.rb
+++ b/app/controllers/open_api/v1/events_controller.rb
@@ -1,32 +1,37 @@
+# frozen_string_literal: true
+
+# authorized 3rd party softwares can manage the events through the OpenAPI
 class OpenAPI::V1::EventsController < OpenAPI::V1::BaseController
   extend OpenAPI::ApiDoc
+  include Rails::Pagination
   expose_doc
-  
+
   def index
-    
-	if upcoming
-      @events = Event.includes(:event_image, :event_files, :availability, :category)
-				.where('availabilities.end_at >= ?', DateTime.current)
-                .order('availabilities.start_at ASC').references(:availabilities)
-    else
-	  @events = Event.includes(:event_image, :event_files, :availability, :category).order(created_at: :desc)
-    end
+    @events = Event.includes(:event_image, :event_files, :availability, :category)
+    @events = if upcoming
+                @events.references(:availabilities)
+                       .where('availabilities.end_at >= ?', DateTime.current)
+                       .order('availabilities.start_at ASC')
+              else
+                @events.order(created_at: :desc)
+              end
 
-    if params[:id].present?
-      @events = @events.where(id: params[:id])
-	end	
 
-    if params[:page].present?
-      @events = @events.page(params[:page]).per(per_page)
-      paginate @events, per_page: per_page
-    end
+    @events = @events.where(id: params[:id]) if params[:id].present?
+
+    return unless params[:page].present?
+
+    @events = @events.page(params[:page]).per(per_page)
+    paginate @events, per_page: per_page
   end
 
   private
-    def per_page
-      params[:per_page] || 20
-    end
-	def upcoming
-	  params[:upcoming] || false
-	end
+
+  def per_page
+    params[:per_page] || 20
+  end
+
+  def upcoming
+    params[:upcoming] || false
+  end
 end
diff --git a/app/controllers/open_api/v1/invoices_controller.rb b/app/controllers/open_api/v1/invoices_controller.rb
index 985f01ba4..373e18910 100644
--- a/app/controllers/open_api/v1/invoices_controller.rb
+++ b/app/controllers/open_api/v1/invoices_controller.rb
@@ -1,12 +1,16 @@
+# frozen_string_literal: true
+
 # OpenAPI controller for the invoices
 class OpenAPI::V1::InvoicesController < OpenAPI::V1::BaseController
   extend OpenAPI::ApiDoc
+  include Rails::Pagination
   expose_doc
 
   def index
     @invoices = Invoice.order(created_at: :desc)
+                       .references(:invoicing_profiles)
 
-    @invoices = @invoices.where(user_id: params[:user_id]) if params[:user_id].present?
+    @invoices = @invoices.where('invoicing_profiles.user_id = ?', params[:user_id]) if params[:user_id].present?
 
     return unless params[:page].present?
 
diff --git a/app/controllers/open_api/v1/reservations_controller.rb b/app/controllers/open_api/v1/reservations_controller.rb
index b1218d992..807716793 100644
--- a/app/controllers/open_api/v1/reservations_controller.rb
+++ b/app/controllers/open_api/v1/reservations_controller.rb
@@ -1,36 +1,33 @@
+# frozen_string_literal: true
+
+# public API controller for resources of type Reservation
 class OpenAPI::V1::ReservationsController < OpenAPI::V1::BaseController
   extend OpenAPI::ApiDoc
+  include Rails::Pagination
   expose_doc
 
   def index
     @reservations = Reservation.order(created_at: :desc)
+                               .includes(statistic_profile: :user)
+                               .references(:statistic_profiles)
 
-    if params[:user_id].present?
-      @reservations = @reservations.where(user_id: params[:user_id])
-    else
-      @reservations = @reservations.includes(user: :profile)
-    end
+    @reservations = @reservations.where('statistic_profiles.user_id = ?', params[:user_id]) if params[:user_id].present?
+    @reservations = @reservations.where(reservable_type: format_type(params[:reservable_type])) if params[:reservable_type].present?
+    @reservations = @reservations.where(reservable_id: params[:reservable_id]) if params[:reservable_id].present?
 
-    if params[:reservable_type].present?
-      @reservations = @reservations.where(reservable_type: format_type(params[:reservable_type]))
-    end
+    return unless params[:page].present?
 
-    if params[:reservable_id].present?
-      @reservations = @reservations.where(reservable_id: params[:reservable_id])
-    end
-
-    if params[:page].present?
-      @reservations = @reservations.page(params[:page]).per(per_page)
-      paginate @reservations, per_page: per_page
-    end
+    @reservations = @reservations.page(params[:page]).per(per_page)
+    paginate @reservations, per_page: per_page
   end
 
   private
-    def format_type(type)
-      type.singularize.classify
-    end
 
-    def per_page
-      params[:per_page] || 20
-    end
+  def format_type(type)
+    type.singularize.classify
+  end
+
+  def per_page
+    params[:per_page] || 20
+  end
 end
diff --git a/app/controllers/open_api/v1/trainings_controller.rb b/app/controllers/open_api/v1/trainings_controller.rb
index ded339d63..277c99626 100644
--- a/app/controllers/open_api/v1/trainings_controller.rb
+++ b/app/controllers/open_api/v1/trainings_controller.rb
@@ -1,3 +1,6 @@
+# frozen_string_literal: true
+
+# public API controller for resources of type Training
 class OpenAPI::V1::TrainingsController < OpenAPI::V1::BaseController
   extend OpenAPI::ApiDoc
   expose_doc
diff --git a/app/controllers/open_api/v1/user_trainings_controller.rb b/app/controllers/open_api/v1/user_trainings_controller.rb
index a8a978391..38f0eab18 100644
--- a/app/controllers/open_api/v1/user_trainings_controller.rb
+++ b/app/controllers/open_api/v1/user_trainings_controller.rb
@@ -1,30 +1,30 @@
+# frozen_string_literal: true
+
+# public API controller for user's trainings
 class OpenAPI::V1::UserTrainingsController < OpenAPI::V1::BaseController
   extend OpenAPI::ApiDoc
+  include Rails::Pagination
   expose_doc
-  
+
   def index
-    @user_trainings = UserTraining.order(created_at: :desc)
+    @user_trainings = StatisticProfileTraining.includes(statistic_profile: :user)
+                                              .includes(:training)
+                                              .references(:statistic_profiles)
+                                              .order(created_at: :desc)
 
-    if params[:user_id].present?
-      @user_trainings = @user_trainings.where(user_id: params[:user_id])
-    else
-      @user_trainings = @user_trainings.includes(user: :profile)
-    end
 
-    if params[:training_id].present?
-      @user_trainings = @user_trainings.where(training_id: params[:training_id])
-    else
-      @user_trainings = @user_trainings.includes(:training)
-    end
+    @user_trainings = @user_trainings.where('statistic_profiles.user_id = ?', params[:user_id]) if params[:user_id].present?
+    @user_trainings = @user_trainings.where(training_id: params[:training_id]) if params[:training_id].present?
 
-    if params[:page].present?
-      @user_trainings = @user_trainings.page(params[:page]).per(per_page)
-      paginate @user_trainings, per_page: per_page
-    end
+    return unless params[:page].present?
+
+    @user_trainings = @user_trainings.page(params[:page]).per(per_page)
+    paginate @user_trainings, per_page: per_page
   end
 
   private
-    def per_page
-      params[:per_page] || 20
-    end
+
+  def per_page
+    params[:per_page] || 20
+  end
 end
diff --git a/app/controllers/open_api/v1/users_controller.rb b/app/controllers/open_api/v1/users_controller.rb
index 46a9bf433..00ac3b6ca 100644
--- a/app/controllers/open_api/v1/users_controller.rb
+++ b/app/controllers/open_api/v1/users_controller.rb
@@ -1,5 +1,9 @@
+# frozen_string_literal: true
+
+# public API controller for users
 class OpenAPI::V1::UsersController < OpenAPI::V1::BaseController
   extend OpenAPI::ApiDoc
+  include Rails::Pagination
   expose_doc
 
   def index
@@ -9,19 +13,17 @@ class OpenAPI::V1::UsersController < OpenAPI::V1::BaseController
       email_param = params[:email].is_a?(String) ? params[:email].downcase : params[:email].map(&:downcase)
       @users = @users.where(email: email_param)
     end
+    @users = @users.where(id: params[:user_id]) if params[:user_id].present?
 
-    if params[:user_id].present?
-      @users = @users.where(id: params[:user_id])
-    end
+    return unless params[:page].present?
 
-    if params[:page].present?
-      @users = @users.page(params[:page]).per(per_page)
-      paginate @users, per_page: per_page
-    end
+    @users = @users.page(params[:page]).per(per_page)
+    paginate @users, per_page: per_page
   end
 
   private
-    def per_page
-      params[:per_page] || 20
-    end
+
+  def per_page
+    params[:per_page] || 20
+  end
 end
diff --git a/app/views/open_api/v1/invoices/index.json.jbuilder b/app/views/open_api/v1/invoices/index.json.jbuilder
index 1ded6c5ce..e4def16bd 100644
--- a/app/views/open_api/v1/invoices/index.json.jbuilder
+++ b/app/views/open_api/v1/invoices/index.json.jbuilder
@@ -1,7 +1,8 @@
 # frozen_string_literal: true
 
 json.invoices @invoices do |invoice|
-  json.extract! invoice, :id, :user_id, :reference, :total, :type, :description
+  json.extract! invoice, :id, :reference, :total, :type, :description
+  json.user_id invoice.statistic_profile.user_id
   if invoice.payment_gateway_object
     json.payment_gateway_object do
       json.id invoice.payment_gateway_object.gateway_object_id
diff --git a/app/views/open_api/v1/reservations/index.json.jbuilder b/app/views/open_api/v1/reservations/index.json.jbuilder
index 04d20bd80..dc4b24e5b 100644
--- a/app/views/open_api/v1/reservations/index.json.jbuilder
+++ b/app/views/open_api/v1/reservations/index.json.jbuilder
@@ -1,18 +1,23 @@
-json.reservations @reservations do |reservation|
-  json.extract! reservation, :id, :user_id, :reservable_id, :reservable_type, :updated_at, :created_at
+# frozen_string_literal: true
 
-  if reservation.association(:user).loaded?
-    json.user do
-      json.partial! 'open_api/v1/users/user', user: reservation.user
+json.reservations @reservations do |reservation|
+  json.extract! reservation, :id, :reservable_id, :reservable_type, :updated_at, :created_at
+
+  if reservation.association(:statistic_profile).loaded?
+    json.user_id reservation.statistic_profile.user_id
+    unless reservation.statistic_profile.user.nil?
+      json.user do
+        json.partial! 'open_api/v1/users/user', user: reservation.statistic_profile.user
+      end
     end
   end
 
   json.reservable do
-    if reservation.reservable_type == "Training"
+    if reservation.reservable_type == 'Training'
       json.partial! 'open_api/v1/trainings/training', training: reservation.reservable
-    elsif reservation.reservable_type == "Machine"
+    elsif reservation.reservable_type == 'Machine'
       json.partial! 'open_api/v1/machines/machine', machine: reservation.reservable
-    elsif reservation.reservable_type == "Event"
+    elsif reservation.reservable_type == 'Event'
       json.partial! 'open_api/v1/events/event', event: reservation.reservable
     end
   end
diff --git a/app/views/open_api/v1/user_trainings/index.json.jbuilder b/app/views/open_api/v1/user_trainings/index.json.jbuilder
index 868d73752..2991feb4a 100644
--- a/app/views/open_api/v1/user_trainings/index.json.jbuilder
+++ b/app/views/open_api/v1/user_trainings/index.json.jbuilder
@@ -1,9 +1,14 @@
-json.user_trainings @user_trainings do |user_training|
-  json.extract! user_training, :id, :user_id, :training_id, :updated_at, :created_at
+# frozen_string_literal: true
 
-  if user_training.association(:user).loaded?
-    json.user do
-      json.partial! 'open_api/v1/users/user', user: user_training.user
+json.user_trainings @user_trainings do |user_training|
+  json.extract! user_training, :id, :training_id, :updated_at, :created_at
+
+  if user_training.association(:statistic_profile).loaded?
+    json.user_id user_training.statistic_profile.user_id
+    unless user_training.statistic_profile.user.nil?
+      json.user do
+        json.partial! 'open_api/v1/users/user', user: user_training.statistic_profile.user
+      end
     end
   end