Now that your Reserve with Google account has been set up, the Google Cloud Project associated with the Google Cloud Project number you entered into the Partner Portal will be granted the necessary quota (1,500 queries per minute) to make calls to the Maps Booking APIs, as soon as the APIs are enabled in the Google Cloud API Console. In order to enable the APIs, complete the following steps: In the API Console, click + Enable APIs and Services, search for Google Maps Booking API, and click Enable.
Then repeat this for the Google Maps Booking API (Dev) version: + Enable APIs and Services, search for Google Maps Booking API (Dev), and click Enable. The Google Maps Booking API (Dev) can be used to access the sandbox environment.
If you are having issues making calls to the APIs, please take a look at this documentation.