Shelly H&T Plus websocket connection fails

I have issues connecting a Shelly H&T Plus to my Home Assistant.

Setup:
Home Assistant
Public IPv4 with (sub)domain pointed to it. Let’s Encrypt enabled and working.
Shelly H&T Plus
Public IPv4 with websocket configured.

Both devices are in different subnetworks but should be reachable by each other.

Config on the shelly:
Websocket “TLS no validation”, wss://domain.eu:8123/api/shelly/ws

I also tried the other SSL options with no success.

The shelly logs the following:

shelly_http_client.:302 0x3ffdfd08: HTTPS GET https://updates.shelly.cloud/update/PlusHT (CA shelly_cloud.pem)
18:31:54
shelly_http_client.:606 0x3ffdfd08: Finished; bytes 421, code 200, redir 0/3, auth 0, status OK
18:31:55
shelly_notification:163 Status change of sys: {"available_updates":{"stable":{"version":"1.0.3"}}}
18:31:55
shelly_http_client.:302 0x3ffdfd08: WSS wss://domain.eu:8123/api/shelly/ws (CA *)
18:31:58
shelly_http_client.:606 0x3ffdfd08: Finished; bytes 240, code 404, redir 0/3, auth 0, status -19: Invalid WebSocket handshake response
18:31:59

Is “Code 404” a http code? (aka “not found”)?

Everytime I try to add the sensor at the home assistant I get “Connection failed”

What can I do to fix this issue.

I have the same problem. How can I fix it?
Thanks