Google Maps shows "For development purposes only"

Google Maps is no longer free. You have to associate a credit card so that you can get billed if your site has requests that exceed the $200 credit they give you monthly for free. That is why you get the watermarked maps.

For more information, see: https://cloud.google.com/maps-platform/pricing/

If you want to use map free like earlier, then create an account with valid details (billing, payment, etc.) google gives $200 MONTHLY CREDIT Which is EQUIVALENT To FREE USAGE