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The error message you received indicates that the on-premises Exchange ActiveSync (EAS) virtual directory did not return a valid response when you sent an empty Bearer token request to it. This could be due to a number of reasons, including a firewall blocking URLs or an issue with the EAS virtual directory itself.
You mentioned that you have already added the Office365 World Wide Services Jason object to allow all URLs and domains on the firewall. However, there may be other requirements that need to be met in order for the tool to work properly.
I would recommend checking the following:
- Ensure that the EAS virtual directory is configured correctly and is functioning properly.
- Verify that the firewall is not blocking any other URLs or domains that are required for the tool to function.
- Check that the tool is configured correctly and that all necessary settings have been entered correctly.
Similar thread please refer to: https://learn.microsoft.com/en-us/answers/questions/440903/test-oauthconnectivity-failt-from-on-premise-to-of
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