Meta Box

It's a bad way to go, but it works for me.

open \meta-box-aio\vendor\meta-box\mb-user-profile\src\Forms\Base.php

if (!$is_valid) {
            $this->error->set(__('Invalid form submit.', 'mb-user-profile'));
            return null;
}

modify to

if (!$is_valid[0]){
            $this->error->set($is_valid[1]);
            return null;
}

add_filter( 'rwmb_profile_validate', function( $is_valid, $config ) {
    if ( 'invitation_verification' === $config['id'] ) {
        if ( '123' !== $_POST['invitation_code'] ) {
            $is_valid = [false,'Error Text'];
        }
    }
    return $is_valid;
}, 10, 2 );

The method I use is wp_die('error text');
rwmb_profile_validate can validate
But it cannot return custom error messages
I wish there was a perfect solution too
Because I don't want to use ajax to validate unique data