How to Fix “Invalid Value [GTIN]” Error of Google Merchant Center?

There are two ways to fix the error:

1. Add the valid GTIN in the products and upload them. GTIN refers to barcodes, UPC, or any other globally acceptable unique identifier. 𝗢𝗥
2. Create a custom profile from the app. And do not map the GTIN attribute with barcodes. Once the custom profile is created, upload the custom profile.