My pi 3 B+ works fine with latest octopi (0.15.1?)when I have a monitor, keyboard, and mouse hooked up
It connects to my wifi, and I can run octoprint.
But... when I start the pi without anything else connected, it does not connect to the wifi.
I believe that the setup file was edited correctly.
Any suggestions?
I think I'd try it with just the monitor connected (removing the keyboard/mouse) to try to isolate what's different... noting that the monitor could show you something during this.
Check your network router to see if the Raspi is connected and has been given an IP address. If so, attempt to remote into it with ssh pi@octopi.local or with ssh pi@192.168.1.20 or whatever has been issued as an IP address.
If the router doesn't allow it to connect to the wi-fi network then I'd put the monitor/keyboard/mouse back on, login locally and run ifconfig to see if the wi-fi is connected.
I had a lot of issues trying to use wifi with the 3B+.. as in it would not always connect even sitting next to the router.. Gave up and ran cat 5 and have had NO issues with connectivity since. I realize that wireless is the draw for a pi.. good luck!