Thanks for your message and welcome to our community. 🙌
Please kindly check the operating systems supported by TeamViewer and the versions on both devices.
If both operating systems are under support and latest TeamViewer versions are used, please try these steps:
Exit TeamViewer or reboot the device
On Windows: Go to Connections -> Exit TeamViewer
On Mac: Go to TeamViewer -> Quit TeamViewer
If it still does not work, I would recommend following the below instructions.
Restart PC on both of device
Uninstall TeamViewer from both devices. Please make sure, to also delete the reg-entries in your Windows: How to uninstall TeamViewer on PC or How do I uninstall TeamViewer on my Mac?
Download TeamViewer afterward directly from our homepage and install it on the two devices again. Do not use any old Setup.exe.
If this issue continues, could you please send through a screenshot of the error message? Hope this could help.
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