WS_DELIVERY_UPDATE Issue error - The Handling unit has already been posted for GR without stock

Hello,

We have a requirement to automate the packing for the HU's in the Outbound Delivery in SAP. I am trying to use BAPI_HU_CREATE + WS_DELIVERY_UPDATE to update the packing details to a delivery created. The HU's are created(BAPI_HU_CREATE + BAPI_TRANSACTION_COMMIT) and I am able to see the entry in VEKP table. Even though i try to pass the correct parameters to the FM WS_DELIVERY_UPDATE , its erroring out with "There is already a Handling unit 10005679 posted for gr without stock". When i check in Vl02n for the delivery I dont see anything packed.

Can anyone help with this as to what are the necessary paramters for the function module or any other ways to achieve this?

Thanks.