I think that you can send gcode commands from the ESP32 to the Duet to execute. Via HTTP or serial connection. I guess that this allows you to send gcode such as setting global variables that your conditional code can access. Others may know more details.

@gustav_seasony the REST API is only applicable when you have a SBC connected to the Duet. When running the Duet in standalone mode, use this API https://github.com/Duet3D/RepRapFirmware/wiki/HTTP-requests.

You have some other problems. Twice there is the sequence:

es after '''S''', expected 3
Done!
Response while disconnected:

The first line is probably part of an error message from the Duet, but Repetier has chopped off the first part. I've no idea about "Done!" but I think that's from Repetier, not the Duet. After that, Repetier seems to think it shouldn't be connected and is surprised to see a response.