Recovery problem of database information

Hello everyone !
I just ask you some help because I have a little problem.

The statement is quite simple, I have an android application or registers users. User information are then sent to a php file that I created one user in a MySQL database.
Once the user creates the database, the user can connect. When trying to connect, another php file hosted on my server will check that fournises data exists in the database to allow or not the connection. Unfortunately, the problem comes from there, in all cases, the connection is refused while the data of the users have actually been created in the database.

To verify the credentials of the user, I’ve used JsonObject but I’m not super comfortable, so I think the problem may come from there but I can’t identify it.

Do you see something that can be the source of my problem ?
I also allow, so, you share my fetchUserData.php.

Thanks for your attention !

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Getting information about internet database is a main part of my job because I am going through a tricky technical project these days. Me and my other mates are getting essay writing services and working exceptionally hard to bring more revolution in the world of technology.