Can’t get V2 to work with tags

Do you want to require both a Category and a Tag, or just Tags alone?

They named the built-in Tags taxonomy post_tag so this leads to some confusion.

Here is what you would do to retain the Category requirement and add the Tag requirement — add the following to your theme’s functions.php file or a must-use plugin file.

function custom_rpc_post_types( $post_types ) {
    $post_types['post']['post_tag'] = array( 'message' => 'Please select a Tag before publishing this post.' );
    return $post_types;
}
add_filter( 'rpc_post_types', 'custom_rpc_post_types' );

Tested and it is working (for me).

Solved it. I was using tag instead of post_tag.

Thank you ??