Additional file-related features and issues within Microsoft Teams for business
Thank you for reaching out to the Microsoft Q&A forum.
To upload a file in a channel or chat, select Actions and apps > Attach file in the compose box, choose the file from your device, and then select Send.
For more information, please refer to this article: https://support.microsoft.com/en-US/teams/files/share-files-in-microsoft-teams
If you're still having difficulty uploading the file, could you please share a few more details?
-Where you're trying to upload it (chat or channel)
-What happens when you try to upload it
-Whether you see any error message, and if so, please share the exact message.
I hope this helps, and I look forward to hearing from you.
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