How to set required message

Hi,

To custom error messages, please use the validation in the meta box settings by coding (not available for MB Builder).

$meta_boxes[] = [
    'title' => 'Meta Box Title',
    'fields' => array(
        ...
    ),
    'validation' => array(
        'rules'  => array(
            'field_id' => array(
                'required'  => true,
                'minlength' => 7,
            ),
        ),
        // Optional override of default error messages
        'messages' => array(
            'field_id' => array(
                'required'  => 'Password is required',
                'minlength' => 'Password must be at least 7 characters',
            ),
        )
    )

];