Which outcome should you measure first?
Start with the reason for the workflow. For enquiry intake, success may mean the responsible person received the required details. For appointment scheduling, it may mean a confirmed appointment exists. Those are different outcomes and need different evidence.
Name the owning record before choosing the metric. A WhatsApp reply cannot prove a payment settled. Use the payment provider’s current record for that result. Likewise, use the reservation or appointment system to verify a confirmed booking.