Detect proxy and VPN using IP address.
IP2Proxy API is a free Geocoding API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.
IP Address Geolocation to Country, City, Region, Latitude, Longitude, ZIP Code, ISP, Domain, Time Zone, Area Code, Mobile Data, Usage Type, Elevation and so on.
Details from ip2location.com.

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Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
The IP2Proxy API is provided by IP2Location (ip2location.com). IP Address Geolocation to Country, City, Region, Latitude, Longitude, ZIP Code, ISP, Domain, Time Zone, Area Code, Mobile Data, Usage Type, Elevation and so on.
Yes. The IP2Proxy API is listed in the Geocoding category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The IP2Proxy API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the IP2Proxy API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The IP2Proxy API is served over HTTPS, so it's safe to use in production.