In my case the Geocoding API was returning Error and I fixed it by removing some Application restrictions I had enabled. No country needed in the end and it works fine.
Just some remarks because I see that many people are struggling with issues like this:
1. Make sure that your GCP project is connected to an active billing account. Once one of my bank cards was rejected but it was not clear on my billing dashboard. I had to enter a new card and follow some verification procedures in order for my new account to be accepted and the maps to work.
2. Make sure you have enabled Geocoding API (converts addresses into geographic coordinates) and not just created a key.
3. Some people mentioned that the maps do not load. Make sure Maps JavaScript API is enabled.
“+Enable APIS and Services” gives the option to enable those.