Google's policy state that when a manufacturer has assigned a barcode, then you are required to fill out the GTIN attribute. Failing to do so leaves your account at risk for a suspension.
Also not filling out all required attributes will reduce your potential traffic.
By following the guidelines, you will improve your standing and potential traffic.
Hope this helps.
Albina, if a product has an MPN or GTIN, it's best practice to enter their value as the relevancy will help campaign performance. However, if a product doesn't have either of these codes, then you can set the identifier_exists field to false, which will allow those fields to not exist, letting the products get approved.
Josh - i need the same help but I am unable to be successful at this. I keep getting rejected from surfaces across google because i have all custom products and google requires me to have either 2 out of the 3, gtin, mpn, and or brand. I am able to make a brand name. But what do i do if i dont have either one of those. I have tried adding a field in my feed for identifier exist and set it to "No" yet i still have no luck and i remain ineligible. Please help