---
title: sync.setRef | Doing Work API
description: Record the id an outside system (like quickbooks) uses for an invoice, payment, refund or customer, so your sync can update it instead of making a duplicat
url: https://doingwork.work/docs/reference/sync-setref/
---

# sync.setRef

Record the id an outside system (like quickbooks) uses for an invoice, payment, refund or customer, so your sync can update it instead of making a duplicate. Send external_id null to clear it. Owner or office, or their agent.

|  |  |
|---|---|
| Who | Agents can call this |
| REST | `POST /v1/sync/refs` |
| MCP tool | `sync_setRef` |
| Writes | yes, send an Idempotency-Key |
| Area | [Shop](https://doingwork.work/docs/reference/#shop) |

## When to use it

Doing Work does not connect to QuickBooks itself. Your agent does the sync, on the schedule the shop picks: daily is a good default, and the shop can ask for more or less often.

## What to tell the owner

Say what you did in plain words and what happens next.

## Input

| Field | Type | Required |
|---|---|---|
| `shop_id` | string | yes |
| `kind` | string (one of invoice, payment, refund, customer) | yes |
| `id` | string | yes |
| `system` | string | yes |
| `external_id` | ['string', 'null'] | yes |

## Example

```http
POST https://doingwork.work/v1/sync/refs
content-type: application/json
Idempotency-Key: 3f1c...

{
  "shop_id": "00000000-0000-4000-8000-000000000000",
  "kind": "invoice",
  "id": "...",
  "system": "...",
  "external_id": "00000000-0000-4000-8000-000000000000"
}
```

## Output

JSON. The response shape isn't published yet; read the fields you need and ignore the rest. Errors are `{code, message, status}`.

## Errors

| Code | Status | What to do |
|---|---|---|
| `invalid_input`, `invalid_token`, `rate_limited` |  | Can happen on any call. See [errors](https://doingwork.work/docs/errors/). |