Failed website verification

Hello, may anyone assist with the problem?

Added https://tercad.com/.well-known/org.flathub.VerifiedApps.txt
But the result is shown as failed: “Failed to connect to tercad.com”.

Any suggestions? Thanks in advance

ERROR: The certificate of ‘tercad.com’ is not trusted.
ERROR: The certificate of ‘tercad.com’ doesn't have a known issuer.

That’s what wget tells me.