SSL connection to HA on Synology Docker

Hello everyone,

Looks like I miss the latest solution to my problem - hopefully someone can help me

I have the following configuration:

router 1: glasfiber router → 192.168.1.254
router 2: ASUS router on 192.168.1.10 → DHCP to network 192.168.178.xxx
Synology NAS on 192.168.178.3

Running Docker on Synology with Home Assistant → reachable on 192.168.178.3:8123

On Synology running certificate for *.myname.synology.me
Reverse Proxy activated https://ha.myname.synology.me and http://192.168.178.3:8123
including websockets (Upgrade/$http_upgrade and Connection/$connection_upgrade)

on router 1 portforwarding:
443 to router 2 443
8123 to router 2 8123

on router 2 portforwarding:
443 to synology 192.168.178.3
8123 to synology 192.168.178.3

Setting home assistant Network:
external https://ha.myname.synology.me
internal: http://192.168.178.3:8123

Now I can access the login screen of HA via https://ha.myname.synology.me - when I log in - the next message:
Unable to connect to Home Assistant.
Retrying in 56 seconds…

By entering http://ha.myname.synology.me:8123/ I’m able to login (insecure)

What’s wrong? can somebody help me? If you need more information, please let me know - hope to solve this problem

Thank you in advance