Problem with Joplin Server add-on (SSL record too long) using DuckDNS (which works fine)

So I am trying to set up this 3rd party add-on: Joplin Sync Server Add-on

Problem is that I think I am not setting up Port Forwarding correctly. I have DuckDNS set up and working perfectly fine. I am configuring the Joplin Server add-on with https://example.duckdns.org/joplin. When I goto Open Web UI it always opens to Invalid origin: http://example.duckdns.org:22300 which tells me Invalid origin: http://example.duckdns.org:22300. If I change http to https it tells me Error code: SSL_ERROR_RX_RECORD_TOO_LONG. I’ve seen this error before when I was setting up DuckDNS and I resolved it by adding

http:
  ssl_certificate: /ssl/fullchain.pem
  ssl_key: /ssl/privkey.pem

to my configuration.yaml, but now since that is there I have no idea what to try.

The official Joplin Server documentation says I need to set up a TLS Reverse Proxy, but it only talks about how this is done with Apache. Isn’t the entire point of Joplin Server becoming an HA add-on so that you don’t need to use Apache? Maybe I am misunderstanding what this add-on actually does.

If anyone could help me I’d really really appreciate it and I will definitely go out of my way to “pay it forward”. Thank you!

I think @poudenes might be the creator of this add-on. I’ve also opened an issue on it’s GitHub page, but I’ve never really had much luck with issues on there. Being able to run a Joplin Server from my HA RPi would be incredibly helpful. Pretty sure the problem is some sort of fundamental misunderstanding of port-forwarding and networking so please forgive me if this is a lame problem. I’m just really not sure what other areas I should be looking into now. It doesn’t seem that many people have installed this add-on, but fingers crossed.