ssl.SSLCertVerificationError: [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify failed: unable to get local issuer certificate (_ssl.c:1056)

TL;DR

The remote website seems to be the problem, not Python. There is likely no fix for this other than to fix the website.

Longer Explanation

The website/server your are dealing with is apparently configured incorrectly. This has nothing directly to do with Python. That said, you can ignore any certificate errors with e.g.:

r = requests.get(url=URL, params=PARAMS, verify=False)

or you can otherwise try to point Python at the missing certificates (as pointed out by @dave_thompson_085 in the comments).

However, this is unlikely to do any good as the server then apparently responds with a 500: Internal Server Error (verified with curl) and a Content-Length: 0, which would seem to indicate an error in the processing of api.php itself (i.e. there is no JSON to process anyway).