Configuration of USG LITE 60AX with external Router

Hey there,

first - thanks for ur help!

My setup:

Ive got a router / modem which connects me with the internet.
I get a dynamic ip from my provider.
This router itself has got an internaly static lan interface: 192.168.178.1
And this router is also my dhcp server from 192.168.178.4 till 192.168.178.100

So, i connected the USG LITE 60AX with the WAN port (of the usg) to my routers / modems LAN Port.
I configured the WAN interface of the USG: 192.168.178.2
I configured the LAN interface if the USG: 192.168.178.3

Nebula can reach the device. Thats fine.

But I cant do anything. Anything "seems to be offline".
The DHCP relay (which I tried) seems not to work from 192.168.178.1, I cant resolve any Host, I cant ping 192.168.178.1 or .2 or .3

I have tried a lot with gateways, static ips, changing the LAN / WAN interface so "what could be right".

Also i have disabled all at traffic management, i have tried anything to go online….

Could please somebody tell me if I tried the right "setup" or could give me a "best practise" setup? Iam sure, iam currently just wrong.

"Infrastructure" —> Image

THANK U!