diff --git a/CHANGELOG.md b/CHANGELOG.md
index 68e466357..7e2bd4923 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,7 @@
 # Changelog Fab-manager
 
 - Fix a bug: unable to show wallet payment mean for invoice
+- Fix a bug: PayZen amount of subscription compute error for Coupon validity per user = forever
 - improvement: remove show_username_in_admin_list setting
 - improvement: show invoice payment method in accounting line
 - [TODO DEPLOY] `rails fablab:setup:build_accounting_lines`
diff --git a/lib/pay_zen/service.rb b/lib/pay_zen/service.rb
index 4f2dfbac6..e9597af0f 100644
--- a/lib/pay_zen/service.rb
+++ b/lib/pay_zen/service.rb
@@ -16,9 +16,11 @@ class PayZen::Service < Payment::Service
     order = PayZen::Order.new.get(order_id, operation_type: 'VERIFICATION')
     client = PayZen::Charge.new
     token_id = order['answer']['transactions'].first['paymentMethodToken']
+    coupon = payment_schedule.coupon
+    amount = coupon && coupon.validity_per_user == 'forever' ? first_item.amount : first_item.details['recurring'].to_i
 
     params = {
-      amount: payzen_amount(first_item.details['recurring'].to_i),
+      amount: payzen_amount(amount),
       effect_date: first_item.due_date.iso8601,
       payment_method_token: token_id,
       rrule: rrule(payment_schedule, first_item.due_date),