Why does recaptcha give an error - invalid key?

Question

reCAPTCHA

Hello! I actually put a captcha on the site, but the fact is that he writes to me that the key is incorrect.
I copied the keys given by Google to the right places, but it does not work.
There is a site on which everything is the same, but it works.

Answer 1

it remains to carefully compare everything and copy again
"everything is the same" including the keys?

Answer 2

Perhaps you chose the wrong version of recapth, because if you have version 3, then the key from version 2 will not work, at least I encountered just such a problem