-snip- ...letting you know there is a problem.
Ah that explains. Had it a few times when solving captchas on my pc and mobile. Solving the captcha on the ipv4 url on pc and could continue again, but took a while before my mobile worked again.
No google recaptcha on mobile phone / tablet, temporary workaround:
Requirements; access to desktop/laptop PC, mailbox or compatible text editor.
With error being present in your entire home network, on all devices, open browser console with your PC.
Error line should be visible and look similar to this:
https://ipv4.google.com/sorry/index?continue=https://www.google.com/recaptcha/api2/anchor%
...only with
much more characters after '%' Copy the entire block of text and send it to your mobile via email. Access this link with your mobile browser and solve additional captcha.
note: it will only work if your mobile device is in the same network as your PC (Wi-Fi). That's it.
IMO much easier solution than using mobile Firefox console addon.