Schema.org GTIN missing

The meta key is called: “_gm_gtin”

Somebody here?

Any support here at all?

Hello @keramikoch

Thank you for contacting the support and sorry for the unwanted delay.

We provide faster support on our website’s support channel.

With that said, you can use this filter to add the GTIN value:
https://rankmath.com/kb/filters-hooks-api-developer/#add-brand-name

Here’s the example code that adds brand value, you will have to change the brand parameter to gtin.

add_filter( 'rank_math/snippet/rich_snippet_product_entity', function( $entity ) {
    $entity['gtin'] = 'GTIN VALUE';
    return $entity;
});

Hope that helps.