Error:20 Unsupported or invalid g-code command found in block

LightBurn Software Questions
2

Just a guess but you likely have your laser configured as a “iLaser” device type.

You need this to be set to “GRBL”.

  1. Push “Devices” button in Laser window
  2. Click the name of your device and then Edit
  3. Select “GRBL” and then continue until setup is completed.

Retest.

If that’s not the issue can you push “Save gcode” and save to a file with a .txt extension and then post the gcode here for review?