I built a free reverse geocoding api about 4 years ago ( https://api.3geonames.org ) Usage grew steadily sometimes crashing the server. So I loaded the software on GCP and AWS Marketplaces. Those needing a dedicated api launched their own servers for a fee. It has made an average pf $500 a month since I made those machine images available on https://3geonames.org/api about 2 years ago.
Yes, of course you can use it. The API is free, does not require an api key. The only issue is when many use it and the server crashes. It runs on a t2.micro free tier EC2 instance.