Build a Delivery Payout Calculation API

Build a payment-service endpoint POST /payout that accepts a delivery worker ID, requests that worker's order-activity sequence for a specified day from an upstream dependency, calculates the payout, and returns the dollar amount.

The base rate is $0.30 per minute. During any interval, the rate is the number of ongoing deliveries multiplied by the base rate. For example, two simultaneous active deliveries earn twice the one-delivery rate during their overlap.

For this practice version, the upstream activity contains an orderId, a START or END type, and a timestamp. Calculate from exact elapsed seconds, prorate the per-minute rate, and round the final daily total to cents once using the agreed monetary rounding rule.

Constraints & Assumptions

• Every valid order has one START followed by one END for the requested worker and day.
• Activities may arrive unsorted; equal timestamps create no paid elapsed interval between them.
• A malformed or incomplete activity sequence causes an explicit error and no guessed payout.
• Money uses exact decimal or integer minor-unit arithmetic rather than binary floating point.
• Upstream URL, authentication, timeout, response schema, day boundary, and response envelope are provided by the assessment.

Clarifying Questions to Ask

• Is pay prorated by second, rounded per order, rounded per interval, or rounded only on the final total?
• Which timezone defines the workday, especially across daylight-saving transitions?
• Can an order cross the requested day boundary, and how is the opening active state obtained?
• What status should the payout endpoint return for upstream timeout, malformed activity, or an unknown worker?
• May the activity response be cached, and what correction or freshness behavior invalidates it?