PHP sqlsrv_connect returning false, but no errors

As the title suggests I'm trying to connect to an SQL database (which has been working for years) and has suddenly stopped working. I'm using PHP and I've created a little test PHP file which literally just tries to connect.

All I get when connecting is a false object, and sqlsrv_errors contains nothing. PHP code is:

<?php
ini_set('display_errors', 1);
ini_set('display_startup_errors', 1);
error_reporting(E_ALL);
sqlsrv_configure("WarningsReturnAsErrors", 0);

$server = "*redacted*";
$connectionInfo = array( "database"=>"*redacted*", "UID"=>"*redacted*","PWD"=>"*redacted*");

$conn = sqlsrv_connect($server, $connectionInfo);

if( $conn === false ) {
    die( print_r( sqlsrv_errors(),true));
} else {
    print("Worked");
}
?>

I don't believe anyone has changed anything but I've since updated the PHP/SQL Driver versions to try and get it working.

I've checked the SQL login by going in directly etc and the server is running on the default port.

All I get back is a blank response (assuming because the sqlsrv_errors are empty)

Environment Details: Website/php is running on IIS on Windows Server 2019 PHP v8.2.10, SQL Driver v5.11 (php_sqlsrv_82_nts_x64)

The SQL server is remote (but on the same subnet/lan) I've tried via IP and name to make sure it's not dns.

To add a few more things I've tried:

• Print "Couldn't connect" before the die - this did print out, so it's getting that far.
• turned firewall off on remote and local servers.
• enabled error reporting on everywhere I can think of in php.ini and in the code

Well.. this is not what I expected it to be.

Turns out we had removed "Domain Users" from the "Users" group within computer management on the server running IIS. IIS is using pass thru authentication so I would guess this is why - even though the actual scripts were using SQL authentication.

Re-adding the Domain Users group has fixed it.