You'll have to wait for someone who has had experience tinkering with that specific router. But don't hold your breath. Each equipment has its own specific way of configuring multi-WAN. If it was something I'm familiar with, like if it's a Cisco, Untangle, pfSense, or even a Fortinet, I might be able to help. It's a UI sort of deal. My suggestion is that you look for a discussion group that specifically caters to this model. FWIW, I've got two comments about the router you chose: 1. TP-Link already listed this model as EoL. 2. It only has 10/100 mbps ports when most modern network devices are at least gigabit-capable, including your AX1500. So even if you have three ISPs that has a combined capacity of over 100mbps, you're still constricted to 100mbps to your LAN. You should've gotten the ER-X like we advised you. That would've afforded you a bit more flexibility. You asked for advice, we gave them to you, but you didn't listen.