IBAN validation in Ultimate Member

I want my members to register using their IBAN. I found some code online and changed it to work with the newest version but I am gettin nowhere. The code just isn’t working and no validation is being made.

Following code I added to the functions.php of my current theme:

function checkIBAN($iban) {
    $iban = strtolower(str_replace(' ','',$iban));
    $Countries = array('al'=>28,'ad'=>24,'at'=>20,'az'=>28,'bh'=>22,'be'=>16,'ba'=>20,'br'=>29,'bg'=>22,'cr'=>21,'hr'=>21,'cy'=>28,'cz'=>24,'dk'=>18,'do'=>28,'ee'=>20,'fo'=>18,'fi'=>18,'fr'=>27,'ge'=>22,'de'=>22,'gi'=>23,'gr'=>27,'gl'=>18,'gt'=>28,'hu'=>28,'is'=>26,'ie'=>22,'il'=>23,'it'=>27,'jo'=>30,'kz'=>20,'kw'=>30,'lv'=>21,'lb'=>28,'li'=>21,'lt'=>20,'lu'=>20,'mk'=>19,'mt'=>31,'mr'=>27,'mu'=>30,'mc'=>27,'md'=>24,'me'=>22,'nl'=>18,'no'=>15,'pk'=>24,'ps'=>29,'pl'=>28,'pt'=>25,'qa'=>29,'ro'=>24,'sm'=>27,'sa'=>24,'rs'=>22,'sk'=>24,'si'=>19,'es'=>24,'se'=>24,'ch'=>21,'tn'=>24,'tr'=>26,'ae'=>23,'gb'=>22,'vg'=>24);
    $Chars = array('a'=>10,'b'=>11,'c'=>12,'d'=>13,'e'=>14,'f'=>15,'g'=>16,'h'=>17,'i'=>18,'j'=>19,'k'=>20,'l'=>21,'m'=>22,'n'=>23,'o'=>24,'p'=>25,'q'=>26,'r'=>27,'s'=>28,'t'=>29,'u'=>30,'v'=>31,'w'=>32,'x'=>33,'y'=>34,'z'=>35);

    if(strlen($iban) == $Countries[substr($iban,0,2)]){

        $MovedChar = substr($iban, 4).substr($iban,0,4);
        $MovedCharArray = str_split($MovedChar);
        $NewString = "";

        foreach($MovedCharArray AS $key => $value){
            if(!is_numeric($MovedCharArray[$key])){
                $MovedCharArray[$key] = $Chars[$MovedCharArray[$key]];
            }
            $NewString .= $MovedCharArray[$key];
        }

        if(bcmod($NewString, '97') == 1)
        {
            return true;
        }
    }
    return false;
}


function um_custom_validate_iban( $args ) {

	if( isset( $args[ 'IBAN' ] ) && !checkIBAN($args[ 'IBAN' ]) ) {
		UM()->form()->add_error( 'IBAN', __( 'No valid IBAN account number', 'ultimate-member' ) );
	}
}
add_action( 'um_submit_form_errors_hook_', 'um_submit_form_validate_iban', 99 );