ACF Google maps field just lets you hook up a field to your Google API account. Now that it’s a paid service, you’ll need to add a payment account to your Google API account. It’s really not much to do with ACF, and not something they can “solve”.
Alternatively, use this field plugin to use OSM, a free alternative:
https://github.com/mcguffin/acf-field-openstreetmap
I am currently swapping all my sites over to use OSM as I can’t justify the Google costs.
