@ChrisShang-4172, Thank you for reaching out. The following error says "Invalid user address", it means that you might not listing the meeting times for yourself but rather someone else. This API would only be able to list meetingTimes for the user who has got the token from Azure AD. In the userId/userPrincipalName section if you put down your own UPN or the UPN of the user who has requested the token from AAD (which is used as bearer token to call this api), it should get you a result and http status 200 Ok.
Please refer to the screenshot below:
Hope this helps.
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