Define the qualifying order
Specify the included sales channel, dates, currency, product scope, order threshold if any, discount interaction, customer condition, payment state, and exclusions. Use the same definitions in customer terms and internal logic.
Separate events from decisions
Order creation can begin evaluation without necessarily completing it. Document which later state confirms eligibility and what happens when an order changes before or after that point.
Preserve a decision record
Store the campaign version, relevant order facts, outcome, timestamp, and reason code needed for support and reporting. Avoid collecting unrelated customer data.