Find the root cause of a bug before writing any fix

Fill in

{{symptom}}

What goes wrong, as precisely as you can say ite.g. Orders placed between midnight and 5:30am IST show up under the previous day in the daily report

{{expected}}

What should happen insteade.g. Each order is counted on the calendar day it was placed in India

{{code}}

The smallest chunk of code that contains the bug, pasted in fulle.g. The groupOrdersByDay function (15 lines)

{{tried}}

What you have already tried or ruled oute.g. Checked the DB timestamps are right; setting TZ=Asia/Kolkata on the server changed nothing

Example input

symptom: Orders placed between midnight and 5:30am IST show up under the previous day in the daily sales report.
expected: Each order is counted on the calendar day it was placed in India.
code:
```ts
// report/groupOrders.ts
type Order = { id: string; createdAt: string; amount: number } // createdAt e.g. "2026-09-23T20:15:00Z"

export function groupOrdersByDay(orders: Order[]) {
  const buckets: Record<string, Order[]> = {}
  for (const order of orders) {
    const day = new Date(order.createdAt).toISOString().slice(0, 10)
    ;(buckets[day] ??= []).push(order)
  }
  return Object.entries(buckets)
    .sort(([a], [b]) => a.localeCompare(b))
    .map(([day, items]) => ({
      day,
      count: items.length,
      total: items.reduce((s, o) => s + o.amount, 0),
    }))
}
```
tried: Checked the DB timestamps are correct (stored in UTC with Z). Setting TZ=Asia/Kolkata on the server changed nothing.