error message: Please check your internet connection or API keys. Zoom API is no

Howdy
I can’t generate working API credentials. Everything is ok for the Oauth credentials, but those sdk don’t work. I don’t think it’s my mistake as the procedure is well illustrated in the documentation and relatively simple. I specify that I tried on 3 wordpress installations, one of which was empty, and on two different hostings. If anyone can help me, thank you. I repeat, I followed both the written guide and the youtube video step by step.

I tried both with free Zoom account and with Zoom Premium account

The page I need help with: [log in to see the link]