I am discovery something a little strange reference the gtin issue. When testing, using the exact same copy of the application, on two different urls, on one of the urls, the script works on the other, (it's an exact copy), it does not.
Now, the only difference I can point out for sure, is the one where it works, its not sending to an eBay Store (just standard listing), the one where it fails to send to eBay, is an an eBay store.
Do eBay Stores require a different configuration when it comes to multiple variations and therefore a different (for example) EAN for each of those variations?
I should also perhaps point out, that where I am sending to just a basic listing, I am not setting EANs (for say multiple colour / sizes) but the item lists successfully.
I should also point out that from both urls I am sending to the exact same ebay category id