Why is POST not being sent from iOS?

Question

iOS

Good day. There was such an embarrassment with the POST php method. I can not understand what's wrong and "big brother" did not help.
There is a simple form that sends two fields (name, phone) to the mail.php file using the POST method. (and the method in this case does not matter). So, when I fill out and submit the form from a computer, everything is processed well, but as soon as I send the form from an iOS device, or rather from an ipad mini 2, nothing happens at all. No mistakes, nothing. There is a simple check in the mail.php file of the type:
if(isset($_POST['send'])){ echo "It's work!"; }
send is the submit name.
So, when sending from an iPad, for ifsome reason I don’t get into the block.
Either my mind went crazy, or I need to learn php again. This is the first time I've come across this. The logs are empty, the output of all errors included. No reaction at all