You have Home Assistant running nicely on your internal network.
You have a Synology Diskstation running.
You have a (sub)domain pointing to your home network IP / Synology.
You have already created a Reverse Proxy rule for Home Assistant.
Edit Reverse Proxy rule for Home Assistant
Since you already made a Reverse Proxy rule for your Home Assistant server, it is reachable from outside your internal network, but you get that error message. Here’s how to solve it.
Open Synology DSM and navigate to Control Panel -> Login Portal -> Advanced. There click on the Reverse Proxy button. You should see your Reverse Proxy rule for Home Assistant, select it and click Edit.
In the modal window click on Custom Header. Now click the Create button and select WebSocket.
Now you should have these two headers added to the configuration:
Upgrade: $http_upgrade Connection: $connection_upgrade
Since we now have the Reverse Proxy configuration set up, we need to tell Home Assistant that a trusted proxy is used. Read more on this in the Home Assistant documentation.
Add the following to your
1http:2 use_x_forwarded_for: true3 trusted_proxies:4 - xxx.xxx.xxx.xxx # IP of Synologyyaml
Now restart Home Assistant, and all should be working!