Manufacturer GTIN not unique, already used at article...

Error:

Manufacturer GTIN {0} is not unique; it is first used (in this file) at article {1}.

Explanation:

Each article from a manufacturer shall have a unique GTIN. The manufacturer GTIN associated with an article is not unique. It is the first to be used with the named article in the import file.

Solution:

Find the duplicate manufacturer GTINs in the import file and correct the incorrect code so that there are no more duplicate codes in the import file.

You can check or request GTINs/GLNs at GS1.