Your code is valid but looks like it has already been used on another site. Why this note?

It is still the same issue than in this topic: Your code is valid but looks like it has already been used on another site. Why?

The topic was closed before we have found the solution due to my not responding. I did not respond, because my hosting broke down. Now the web is back online and I am still experiencing the note that the validation code is already in use, which is not possible.

Hi Kamil,

Unfortunately, your website Admin URL is not accessible and showing the ERR_INVALID_RESPONSE error. Can you please let us know once it is accessible?

Thanks