Message selector has a very similar interface as the one for SAP PI/PO - refer to int4 IFTT Message Selector.
On the selection screen you will see two additional fields:
Store ID (content) - ID of the store block in the IFlow (if exists). Stored payload from this block will be fetched.
Block ID (content) - ID of the block in the IFlow where payload will be fetched from. Remember, that payload is stored on the block BEFORE processing.
If there is no store block in your iFlow remember to turn on the trace option before message processing.
CPI Trace can be enabled directly from int4 IFTT Cockpit. This option is available if there is at least one landscape configured with CPI.
Schema:
