Problem with CI3, PHP8 and AJAX

Morning

Do AJAX requests in PHP 8 work normally with CodeIgniter 3?

I installed an application under CodeIgniter 3 which works perfectly since a long time under PHP 7.4. I want to install the same application in another machine running PHP 8.1.2. And there the AJAX requests no longer pass

Does anyone have a solution or has had this problem before?

Thank you