We track local listings with both the URL and the GMB name.
In the case that there is no website URL listed, we will try to match the GMB name.
Google Organic Listings (Snack Pack)
As you can see below, certain results will not return a website URL, but instead have a GMB (Google My Business) name instead.
Google Local Maps
In the case of the "website URL" being present, we will track by GMB name and also the URL.
However, if there is no "website URL" returned in the results, we are forced to use the GMB name to track rankings.
Update Existing Keywords
Tracking GMB without a URL
To track a listing using the name only (if you don't have a website) you can use the share URL of the listing as the URL. e.g. https://g.page/mybusiness. You can remove the '?share' that is included when you click share from the Google listing.
Example of how it should look: