Gravity Forms compare fields to make sure they don't match
add_filter( 'gform_field_validation_1_91', function ( $result, $value, $form, $field ) {
$master = rgpost( 'input_7' );
if ( $result['is_valid'] && $value == $master ) {
$result['is_valid'] = false;
$result['message'] = 'Please enter a name.';
}
return $result;
}, 10, 4 );