I was able to setup it between a Fritzbox 7530AX (FritzOS 8.02) and a RT-AX58Uv2 (gnuton merlin, but was also working with stock Firmware) by starting the process on the Friztbox (acting then as the server, creating the ) and then import config into the Asus
Step 1
In the Friztbox wizard, just...