Zend certified PHP/Magento developer

Magento 2, A technical problem with the server created an error. Try again to continue what you were doing. If the problem persists, try again later

Hope everyone is good.

I saw other threads with similar issues but mine is different.
It is happening when I am trying to create or update a coupon with specific customer groups.

It gives me an error A technical problem with the server created an error.
Try again to continue what you were doing. If the problem persists, try again later.

Please anyone can help?