The three second delay did not work either, alas. We still have missing deals 
The problem only occured after re-syncing our mappings JSON file. We’ve reverted that and the issue remains. Open to suggestions - the API just does not work reliably for us any longer. If we check the USPERTS with a sync, we see:
{“status”:“error”,“message”:“No sync messages found for DEAL 1234 in Our Store”,“correlationId”:“826babf6-1bf3-4b1d-9431-a2e24c52a731”}
Funny thing is that some deals with errors still get in to the system, and some do not. How to debug that? Is there are more detailed way to get the error for a particular object?
Finally, can the payload for the UPSERT contain all of the objects together in one JSON structure?