Hi @Ilkiz, Heiko,
Thank you for posting in this community.
I am not quite sure what language you are using for the document libraries on Shared Teams Channel and on SharePoint Online.
The only requirement for csv files is to be in UTF-8 encoding.
If the URL and name of the file repository in your Shared Teams Channel is in English, then you should use English. If the URL and name of your document library on SharePoint Online is in German, then you should use German. Just make sure that the URL and name in the file match the URL and name of the file library so that SPMT can correctly find the corresponding file library.
You can also have your colleague use different accounts and computers to test if he needs to adopt a different language as well.
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