UPC/GTIN/GS1 Troubles

I’m trying to list a product from Alibaba on my seller account (first time). I’m having a hard time figuring it out..

From what I understand I need to buy a GS1 which is fine, the product came with its own barcode from the supplier. On the app, Amazon says the UPC I entered doesn’t match the product I’m listing.

So I guess my question is, what am I doing wrong? Do I need to buy a gs1 and physically put a new label on every item? I’m super confused and would appreciate any help