I have no idea why my reply never got sent 4 days ago, but here it is:
I’m guessing that your Canasta instance is not publicly reachable. What has happened is: Caddy tried to auto-generate a TLS certificate for your site, but failed because it could not reach your site for verification purposes. If you are fine with not using HTTPS, you could try to visit your website using plain old HTTP if your browser allows for it. Otherwise, you’ll need to manually generate a TLS certificate and install it on Caddy, which I’m not familiar with, but I’m guessing should be possible.