"This operation is not supported for unclaimed locations" Error Message

This error message occurs when attempting to respond to a review for a location that has been marked as unclaimed by Google. A locationState can move from a claimed to unclaimed status for any number of reasons, and unfortunately, it is not shared with us.

Resolution:

There are a couple options for re-establishing your connection, but first you must find out if your location is simply unclaimed or if you've just lost ownership.

If the latter, then you may need to either ask to be added back as an admin or you may need to request ownership to re-establish your connection.

If it is the former, then you must go through the process of claiming it again. You can start this process by,

Logging into your GMB portal and going to "Add new location",
Search for and claim your location