Post is always empty on live server

Hello,
I put up my website on the prod server and there way the following problem:
When sending a form with method POST, nothing is received in the controller.

---

Informations:

• When checking the developper tools of my browser, I see the request is sent with the correct method (POST) and the data are present.
  
• When writing
  
  Code:

  var_dump($this->request->getPost())
  or
  
  Code:

  var_dump($_POST)
  in the controller, an empty array is displayed.
  
• If I try to do the same request with Postman, the result is the same.
  
• When trying a simple PHP page that doesn't use the Framework, everything works fine ⇒ it's probably CodeIgniter's fault (or, more plausibly, my configuration).
  
• Everything Works Fine on My Machine™, but it doesn't in the server (well, the rest does, only the POST content is lost AFAIK).
  
• The server is hosted by OVH.
  
• The code has been tested with both PHP 7.4 and PHP 8.0.
  

Any chance one of you knows what I'm talking about and has a solution to explain? I'm willing to provide extended informations upon demand.

Thanks to whoever takes some time to answer!