After adding the app to the store is complete, you need to embed the app in the theme:
Go to Theme setup from the left sidebar -> Select the theme you want to apply -> Click the "Go to Theme Editor > App Embeds" -> Click the Save button in the upper right corner.
If you want to preview the app on an unpublished theme, then follow the same steps as above.
We recommend that you create your own Google API Key to ensure that the app works properly and smoothly (About 5 minutes to complete this).
--> How to generate Google Map API Key: https://sl-guide.storeify.app/google-map-api-key/generating-and-setting-api-keys
Note: You need to enable the list of required APIs and enable billing on the Google Cloud Project.
Don't worry about the cost when using Google Maps service, currently Google free $200/mo for each account (about 28.5k maploads/mo): https://mapsplatform.google.com/pricing/