connection cannot be established reason unknown

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I have a friend in India trying to remote into my computer in Canada. We have done this many many times, however, after a clean install of windows 10 pro on my machine, he cannot connect to my machine in Canada.... the error is "connection cannot be established reason unknown".

I can connect to his machine no problem. We have both tried downgrading versions. Disabling IPV6 also UPD in TeamViewer and nothing works. I have tried having connections from others in Canada and no issues... even from android phone I connected to my system fine. 

I believe it must be on his end but would appreciate any suggestions to fix the issue.

 

Thanks and Regards,

Steve