AiMesh can't find node

I have three RT-AC88U routers. One I have setup in AP mode on my own network (since Google Fiber requires using their own router). Another I have setup as the router at my parents' home. The third I just bought to add as an AiMesh node to my parents' network (so as to extend the Wi-Fi coverage out by their pool).

I live in a different state, so I had the new router shipped to my home, where I set it up and tested the AiMesh setup process on my own network. It worked great. The process was...

AiMesh can't find node