Here are a few things that may help:
Check that your application.yml has something similar to the following:
MQTT_HOST: "192.168.1.100"
API_HOST: "192.168.1.100"
PORT: "3000"
And you are running:
/mqtt-gateway$ WEB_API_URL=http://192.168.1.100:3000 npm start
/Farmbot-Web-App$ npm run dev
(Since you are running MQTT on the same server, you could probably just run npm start in /mqtt-gateway and npm run dev in /Farmbot-Web-App, but either approach should work.)
For SERVER during FarmBot OS configuration: http://192.168.1.100:3000.
After you have completed FarmBot OS configuration, if you restart MQTT at any point, you will need to power cycle your device to reconnect it to the app. When you do, do you see something like this in the terminal for the app?
Started POST "/api/tokens" for . . . (there’s a long string in the request, so it should be easy to spot)
If you don’t, the device isn’t connecting to the app, and will not connect to MQTT either. You should also see that POST after pressing SUBMIT during FarmBot OS configuration.