How to configure this kinda ASYNC scenario in SAP PI 7.0

Hello Experts,

We have to configure the process as shown below in SAP PI 7.0.

Non-sap system will send data to SAP PI (step 1A), the status of that message in SAP PI should be send to sender system (i.e. if the message failed in PI or was successful in PI) (Step 1B)

SAP PI will send data to ECC for update via proxy class (step 2) ...

After Update in ECC (successful or error) the status should flow to SAP and then to NON-SAP (step 3 and 4)

We are very clear about how to achieve step 1A, 2, 3 and 4, but how can step 1B be configured in ASYNC process?