Syntax errors...
Lines 66 & 72 need terminating semicolons.
Logical errors ...
1. This needs error handling, at the very least ...
$con = new mysqli ($dbServer, $dbUsername, $dbPassword, $dbSchema)
or exit( mysqli_connect_error() );
2. Select * is inefficient. Query only the expressions needed.
$sql = "SELECT * FROM ProvidersAccounts WHERE `LicenseNumber` = '" .$licenseNumber."' ";
3. This is wrong:
$licenseValid = mysqli_query($con, $sql);
mysqli_query() returns a resource even if the query returns zero rows. Var names should be self-documenting. You need error handling in all Db calls...
$res = mysqli_query($con, $sql) or exit( mysqli_error($con) );
Those problems also occur in the next query.
Re debugging, see
http://blog.teamtreehouse.com/how-to-debug-in-php for a nice summary of basic debugging methods.
There are many open-source and commercial PHP debuggers, I've only tried a few of them. Some just offer syntax checks by spawning a PHP run on the file and reporting the syntax errors. Others offer breakpoints &c, eg
https://xdebug.org/docs/index.php?action=index.
My preference is to use a general-purpose programmer's editor for all languages I write. I use NotePad++, which can be taught to run PHP on a source file and report syntax errors, and to suss out bugs I add in reporting stubs (eg echo in PHP) to track var values. Chacun à son goût.