The receipt_type 'DECOMMISSION' is generated on our side if a cash register has been set to DECOMMISSIONED.
Once a cash register has eventually reached its end-of-life this has to be reflected by setting its state to DECOMMISSIONED. Decommissioning a cash register creates a final receipt / decommission receipt ('Schlussbeleg') and a message to FinanzOnline (FON) with the information that this cash register is now decommissioned.