If you don't have UPCs and GTINs etc can you just assign fake ones?

Like a numerical sequence 0001... 0002.... 0003 etc.

Or do they validate them in some database before you use them.

So far we have just been assigning  the "does not apply" option because that suits our particular category.

I know on Google Merchant, where it is compulsory, you can just assign a fake number sequence to satisfy the field.