Make GTIN mandatory

Hello

I’m super stuck – I’m trying to make it mandatory for Admins to add the GTIN number, to make it *required. I found this code for making SKU’s mandatory and it works really well. I’ve been trying to customise it so it makes the GTIN mandatory but with no luck. He’s a link to the code for the SKU.

Any help would be greatly appreciated!

https://stackoverflow.com/questions/66463379/make-sku-mandatory-in-woocommerce-before-publishing-a-product