Thanks for the quick response. I have already been able to setup (via LAN) Archer ZR1600v is the primary modem/router and the ASUS DSL AC68U is the secondary router (mode) as a slave.
I need to bridge them via WiFi so I can use the ASUS at the other end of the house where the Solax Inverter is. I would like to know how to setup both for the WiFi bridging.
The WDS or WiFi bridging is not possible with your TP-Link VR1600.
This means that you are not able to connect them via Wireless.
You may consider a Mesh network or a longer cable to relocate your ASUS router near the Solax inverter.