All maps in the site don't show up

None of the maps show up in the site (about and centers pages).

The console shows an error prompting you to enable billing.

I suggest using the SKU basic embed which is free without limits right now:
https://developers.google.com/maps/documentation/embed/usage-and-billing#embed

You can easily get a basic embed for a location using google maps search and then choosing share -> embed (which will get you the free iframe).

The only problem is that you might not be able to get a map like the one in the about page with multiple locations in the same map.