Auto-discovery services suggest URL: This error indicates that we were unable to connect to the Source system using the Source URL specified on your connector. We then queried Exchange auto-discover services, which responded with an suggested URL. This error message is asking you to check if the suggested URL is correct and, if so, to update your configuration.
Resolution:
Check if the suggested URL points to the Source. For example, if auto-discover settings already point to the Destination system, then the suggested URL will be incorrect as a Source URL, and so should not be used. Otherwise, try specifying the suggested URL on your connector as the Source URL and resubmit mailboxes for migration.