Buy course plugin : 404 error when confirming order with a discount coupon

[losbit]

Describe
When a student uses a coupon in a course and confirm the order with any payment method gets a 404 error in https://{domain}/plugin/buycourses/src/process.php

To Reproduce
Steps to reproduce the behaviour:

1. Go to course catalogue
2. Click on a course which costs $10 (for example)
3. Apply a $10 or any coupon to get a total or partial discount
4. Then click on Confirm order with any payment method in https://{domain}/plugin/buycourses/src/process.php?i=1&t=1&c=free
5. A 404 Not Found error page is displayed in https://{domain}/plugin/buycourses/src/process.php

Expected behaviour
To process the purchase with a $0 or partial cost.

Screenshots
No screenshots necessary.

Desktop (please complete the following information):

• OS: Windows 11
• Browser: Chrome, Firefox, safari, Edge

**Server

• OS: Debian GNU/Linux 11}
• nginx/1.24.0
• Version of Chamilo: 1.11.26
• Version of PHP: 7.4.33

Additional context
Rewrite in nginx is well configured as in https://11.chamilo.org/documentation/installation_guide.html#16._Rewrite
There are no other problems in Chamilo LMS.