Require user to input code from an array of allowed codes with Gravity Forms [closed]

by

Try below code:

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;
}

Further, You can review validation in more detail from this url