Hi ES George,
The standard SAP Third-Party process does not cover this scenario as it does not contain any delivery documents. So you need to get creative. You can evaluate the following options:
Option 1)
Instead of using the Third-Party process (item category TAS), check out the process 'Individual PO' (item category TAB). The sales order will create a PR and PO. After the MIGO, the goods are in stock. You can create an outbound delivery based on your sales order. Then, pick, pack, PGI and create the customer invoice. Your current process uses the vendor's EDI to pick and pack the delivery. You will need to enhance the process and execute the MIGO on the PO before SAP executes pick and pack.
Option 2)
In addition to the standard Third party documents, create an outbound delivery based on the sales order. You will need to adjust the configuration to achieve this. Copy the schedule line category CS and make it delivery relevant. Adjust the delivery item category and schedule line category determination accordingly. The item category in the delivery must not be picking relevant. You will need to test what happens at Goods Issue - it must not generate any financial posting.
Bernhard