3DPrint evaluates the geometry of the part to determine if there is enough powder in the Feeder to complete the build. If not, 3DPrint displays ADD POWDER in the Printer Status dialog. You cannot start the build until you add powder to the Feeder.
Do not add powder unless all of the powder in the Build Bed, Overflow (front and rear), and Deck has already been returned to the Feeder, via a vacuuming operation.
For details on adding powder, refer to the User Guide for your printer.