Own GTIN is not unique...

 
 
Error:
The own GTIN is not unique. It was used first in the import file for the article in question.
 
Explanation:
Your own GTIN is not unique. It was used first in the import file for the article in question.
 
Solution:
Each article must have a unique GTIN. Find the double GTIN numbers and correct them so that there are no more double GTIN numbers in the import file.
You can check or request GTINs/GLNs at GS1.