I’m also struggling to access HA from external URL.
So far I get the HA login prompt on the ‘external device’ but when I enter my credentials I get a message: ‘Unable to connect to Home Assistant’, Retry
I believe it has to do with the SSL certificates, but correct me if I’m wrong.
From my Synology NAS I downloaded the SSL certificates. The zip had 4 files:
privkey.pem
syno-ca-privkey.pem
syno-ca-cert.pem
cert.pem
I tried to use both (privkey.pem with cert.pem and syno-ca-privkey.pem and syno-ca-cert.pem) individually in the configuration. Copied the files in the SSL folder and performed a ‘Configuration Check’. Check passed successfully but after restart of HA, it’s not accessable at all (internal and external).