Magic DNS, firefox doesn't recognize ssl cert on Synology DS?

First of all: Great piece of Software tailscale that is. I love it! Thank you so much!

But right now I’m heading a problem I wasn’t able to solve myself yet:
The topic almost says it all… I wanted to make use of the magic DNS feature and followed the instructions on the knowledge database for magic dns usage:
I logged into my Synology Diskstation via ssh and did “sudo tailscale cert” what was confirmed with "For domain, use “xyz.magic-dns-domain.ts.net”.

when i try to log on the user interface via https://xyz.magic-dns.domain.ts.net:port (the port set for DSM interface) in my firefox browser resolves the domain name correctly, but it won’t recognize the ssl cert and says the domain is insecure…
when I acknowledge that it let’s me pass on to the login interface, but not ssl secured…

Any suggestions what i could have done wrong?

Greetings
nascherer

—> Post can be deleted… was to dump to actually add desired domain that should get a certifcate in the command line, so nothing really happend.
After adding the device.ts-domain private pem and crt were generated and could be implemented by hand in DSM…now it works