firmware/docs/known-issues.md

Known issues

OrcaSlicer sends a 3MF file instead of G-code

Some OrcaSlicer profiles can upload a .3mf project rather than the sliced .gcode file. Reforge expects the G-code file for printing, so the job may not appear or start correctly in Mainsail.

In OrcaSlicer, open Printer Settings, change the upload protocol from FlashForge to Moonraker, and uncheck:

Use 3MF instead of G-code

Slice the model again and upload the resulting .gcode file through the Moonraker upload target.