# company.shareholders.taxNumber

Save or remove a shareholder's tax number for Schedule 50 and T5 slips: { holderId, kind (sin, bn with an optional program account, itn, or foreign with country), value, country? } or value null to remove it. SINs are checked with their check digit. The number is stored encrypted and only ever returned masked; it is never logged or audited.

`POST /api/v1/accounting/company.shareholders.taxNumber`

Permissions: `accounting:read`, `accounting:write`, `accounting:admin` · Roles: admin

MCP tool: `accounting_company_shareholders_tax_number`

## Fields

| Field | Type | Required | Notes |
| --- | --- | --- | --- |
| `holderId` | string | Yes | Matches ^[a-z0-9][a-z0-9-]{7,39}$. |
| `kind` | enum |  | Which kind of record or job this is. One of: `sin`, `bn`, `itn`, `foreign`. |
| `value` | string or null | Yes |  |
| `country` | string |  | exactly 2 characters. |

## Example request

```bash
curl https://app.getoatmilk.com/api/v1/accounting/company.shareholders.taxNumber \
  -H "Authorization: Bearer $OATMILK_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
  "holderId": "aaaaaaaa",
  "value": "example",
  "kind": "sin"
}'
```

Reference page: https://app.getoatmilk.com/docs/api/company.shareholders.taxNumber