请尝试以下代码：

add_filter( \'gform_field_validation\', \'custom_validation\', 10, 4 );
function custom_validation( $result, $value, $form, $field ) {
    $arrWhitelist = array(\'XH6D\', \'8U2A\', \'L9D3\');
    if ( $result[\'is_valid\'] && !in_array( $value, $arrWhitelist )) {
        $result[\'is_valid\'] = false;
        $result[\'message\'] = \'Please enter a value less than 10\';
    }
    return $result;
}