Google has updated its product structured data document to specify that the GTIN value must be presented is in numerical form. Google said it does not support the URL form for GTINs.
You can see the update in this location of this Google help document where Google added “Make sure the GTIN value is in the numerical form; we don’t support the URL form for GTINs.” That line was previously not there, as you can see from the Wayback Machine archive.
Naomi Gallula notified me of this on Twitter and said that Google now only supports the numerical value despite Schema.org saying GS1 digital link is okay. Here is her tweet:
🚨 Google made an update on the Product structured data documentation- For GTIN, Google only supports the numerical form of the GTIN and not the GS1 digital link as specified in https://t.co/5qDnTnhDJd.
FYI- @rustybrick pic.twitter.com/EHPOxqzt7G
— Naomi Gallula (@naomig84) August 8, 2022
So keep this in mind when implementing GTINs, which is important for product search in Google.
Forum discussion at Twitter.