Hi,
The inbound delivery that is created here tries to receive an HU into a WM managed warehouse. The problem why the error message L3 209 is triggered is that the HU already exists (it was created in an HU managed storage location which was not WM managed) but the storage unit does not exist. In this case because of the HU existence the SU is checked in table LEIN as well and the message is send if it does not exist. You should allow that the goods receipt can be posted before the TO is created and then post the GR first. This posting will then also create the storage unit in table LEIN and the TO creation will work properly.
You can allow the GR for the delivery before creating and confirming the TO by setting the following flag in customizing for the warehouse: "Goods movement for delivery occurs before transfer order" (field V_TVLR-XWBTA). This field is currently set only for the delivery item category for the warehouse AF1 but you can set it also in general for this warehouse. You can find and set this under the customizing path:
SPRO -> Logistics-General -> HU management -> Basics -> Delivery -> Define Sequence of Transfer Order - Goods Receipt.
Please have a test in the development system to check if it works or not.
Best regards,
Edward