Hi @ralphsomeday 

Good questions.

• Are the incoming messages queued?
  • No, they are processed in real-time, and can run in parallel
  • There is an option to add a Delay After Queue step to Zaps: https://zapier.com/help/create/customize/add-delays-to-zaps#delay-after-queue
• Is the order of processing in Zaps guaranteed?
  • Yes and no
    • Yes, can be controlled using the above mentioned Delay After Queue
    • No, there can be issues with apps in Zaps, Zapier, etc. that may cause hiccups/glitches and results in a backlog of Zap Runs to be processed, which when fixed may not process in sequential order
    • System Status can be checked here: https://status.zapier.com/
• What if there is error in the process of zap?
  • The Zap Runs will show how a Zap processes
  • There is an option to replay failed Zap steps: https://zapier.com/help/manage/history/replay-failed-zap-runs
• Can I use the request_id from the webhook to lookup zaps execution
  • No, the Webhook request_id is not an available data point to use to lookup in the Zap Runs: https://zapier.com/app/history/
  • There is an existing feature request open for this