Hi, PatrickMacH.
Can you add supporting for www. domains?
I see https://paperwallet.611.to - is opening good.
Also  https://www.paperwallet.611.to - is opening good, too.
But...

https://be.611.to - is opening good.
https://www.be.611.to - Web-page is not available, or another site is opening.

I just tryed to get free SSL certificate here: https://www.sslforfree.com/
And I did verify my domain name, using "Manual Verification".
Then I did upload that file, in "/.well-known/acme-challenge/" folder.
To create "/.well-known/"-folder on windows, I did use the command:

Then, this service return me SSL certificates.
But... Is see this was been registered to www.blahblahblahblahblahblahblah.611.to, not for blahblahblah.611.to
So this seems, like invalid certificate.

P.S.: ZeroSSL also provide the SSL certificates for www.domain.name, not for domain.name