One widget, different reviews per page
Dynamic Sources lets one widget display different reviews depending on the page it is on.
Showing more than one Google location
The Google Reviews app takes one Google Business Profile per widget.
The short answer
The Google Reviews app takes one Google Business Profile per widget. It cannot combine two locations.
The All-in-One app can — it accepts up to 100 sources, including several Google profiles in the same widget.
Showing several locations together
Use All-in-One and add each Google profile as its own source. Source tabs let visitors filter by location if that is useful, and the overall rating is calculated across what is connected.
Showing a different location per page
That is Dynamic Sources, an Enterprise feature — one widget whose content varies by page, so each location page shows its own reviews without building forty widgets. More on it here.
Which to choose
Two or three locations shown together: All-in-One with several sources. Many locations each on their own page: Dynamic Sources. One location: the Google app is simpler and cheaper.
Questions
Other common problems
Widget isn’t showing at all
Six causes, in the order they are worth checking. Most cases are the first three.
Adding a review source
Most sources connect by pasting a link to your public profile on that platform.
Error while collecting reviews
Two error messages can appear when you add a source.