POST request not going through?

I found that it didn’t work because both endpoints used the same route.
I expected defining one for POST and one for GET would result in different callbacks, but they apparently conflict with each other.

In a first time, I get the request going through simply by change the namespace for the POST.

Maybe there is a way to define different callbacks far a same namespace , I need to check that.

(Now, I have another problem which is that $data input is empty, but I need to check things and maybe make another question for that.)

error code: 523