NR5101 Routing

Hi, im using my NR5101 as Access Point. It has a static IP Adress und DHCP is set to relay. I also want to use its 5G and set it up as Failover.

Config:

NR5101: 192.168.88.3; ROUTER: 192.168.88.1

I created a simple test with 1.1.1.1 as DEST and the NR5101 as Gateway. It does not work. Packages are dropped.

Question: What do I miss? Any config I have to to at the NR5101? It has 5G connection of course.