Problem with "you need to add a GTIN or MPN"

[ukseller44]

Hi everyone,

I have listed all of my products and will promote them with google ads. However they don't get approved by google. It says "you need to add a GTIN or MPN"

I have listed them as "Custom item" so it shouldn't ask for GTIN or MPN however it keeps asking it.

Do you know why this is happening? Any recommendations? 

Thanks in advance