DIAGNOSIS This is almost always a signal strength issue. The opener's radio isn't as powerful as your phone's, and your router might be too far away or blocked by too many walls.
FIX First, move your router closer if possible, or use your phone as a hotspot to test. The official steps: 1) On the wall console, hold the 'wifi' button for 6 seconds until the light blinks. 2) On your phone, go to wifi settings and connect to the opener's network (it'll start with 'Chamberlain'). 3) Open the MyQ app, it should guide you to select your home network and enter the password. The trick is to be standing in the garage with your phone during this. If it fails, power cycle the opener (unplug for 30 seconds) and try again.
IF THAT DIDN'T WORK Some older routers or those using certain security types (like WEP) aren't compatible. Make sure your home network is using WPA2 or WPA3 security. Also, if you have a mesh network system, sometimes the band steering causes issues. Try temporarily creating a separate 2.4GHz-only network for the opener, as it doesn't connect to 5GHz bands.
HEADS UP The opener needs a constant 2.4GHz signal. If your router is in the far corner of the house, a simple wifi range extender plugged in an outlet nearer the garage often solves it for good.