how to send post request from APK with MIT app inventor?

I'm new here - I used to find answers only without making account haha .. I'm creating an android App using MIT App inventor online. I created sign up form and I want to connect it with a MySQL database on my web hosted website.. I actually have two question now, the first is general and the second is specific for my case..

  1. when sending with GET request using php $_GET over HTTPs is it risky or it doesnt matter since it's encrypted connection ? and what about when sending GET requests from an APK ? can data be tracked ?

  2. I watched a tutorial for sending data to database from MIT App inventor, they created a PHP file that fetches the variables submitted from the app with $_POST then inserts them into the DB, but it was on localhost "both the app and the server where on same host".. in my case I want to send the form data to my php file on my web host, I tried the same method to no avail.. what can I do? another tutorial worked out but he used $_GET in the php, is it safe ? is there a way for the $_POST to work..

Sorry for the long question, Im beginner ..

THANKS