Hard to tell really without a sample URL. Please show what sitekey was delivered for what URL and I debug it.
It's SER sending these requests?
ok, I think it's about the recaptcha key being v1 which is discontinued on the sites you sent me. So submission is impossible there now. I will have to skip that on next update.
The alleycorner.com and metcalfeshaver.com examples give recaptcha errors if you look at them in a browser, its pretty common for site owners not to set up recaptcha properly.
In most cases it's a mix of recaptcha v2 and v3 site key being used on the same page. SER extracts one of them (same format, same length) and later doesn't know which system to use. Indeed samples of pages where this happens would help.