curl -X PATCH https://thepostalcompany.com/api/v1/letters/a1b2c3d4-e5f6-7890-abcd-ef1234567890 \
  -H "Authorization: Bearer tpc_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Dear Jane,\n\nUpdated letter content.\n\nBest regards"
  }'

{
  "id": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "status": "draft",
  "recipient": "Jane Doe",
  "address": {
    "street": "Keizersgracht",
    "number": "123",
    "postalcode": "1015 CJ",
    "city": "Amsterdam",
    "country": "NL"
  },
  "content": "Dear Jane,\n\nUpdated letter content.\n\nBest regards",
  "created_at": "2026-04-14T10:00:00.000Z",
  "updated_at": "2026-04-14T10:01:00.000Z"
}

{
  "error": "Only draft letters can be updated"
}

{
  "error": "Letter not found"
}

PATCH

api

letters

{letterId}

curl -X PATCH https://thepostalcompany.com/api/v1/letters/a1b2c3d4-e5f6-7890-abcd-ef1234567890 \
  -H "Authorization: Bearer tpc_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Dear Jane,\n\nUpdated letter content.\n\nBest regards"
  }'

{
  "id": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "status": "draft",
  "recipient": "Jane Doe",
  "address": {
    "street": "Keizersgracht",
    "number": "123",
    "postalcode": "1015 CJ",
    "city": "Amsterdam",
    "country": "NL"
  },
  "content": "Dear Jane,\n\nUpdated letter content.\n\nBest regards",
  "created_at": "2026-04-14T10:00:00.000Z",
  "updated_at": "2026-04-14T10:01:00.000Z"
}

{
  "error": "Only draft letters can be updated"
}

{
  "error": "Letter not found"
}

Update a Draft

Update a letter that is in draft status. You can modify the recipient, address, content, or any combination. Letters that have already been sent cannot be updated.

Path parameters

string

required

The unique letter ID.

Request

All fields are optional — only include the fields you want to change.

string

Name of the recipient. Maximum 30 characters.

object

The recipient’s postal address. If provided, all required address fields must be included.

Show address properties

string

required

Street name.

string

required

House/building number.

string

Address suffix or addition.

string

required

Postal or ZIP code.

string

required

City name.

string

required

ISO 3166-1 alpha-2 country code.

string

The letter body text.

Response

Returns the full updated letter object (same shape as Get a Letter).

Examples

curl -X PATCH https://thepostalcompany.com/api/v1/letters/a1b2c3d4-e5f6-7890-abcd-ef1234567890 \
  -H "Authorization: Bearer tpc_your_api_key" \
  -H "Content-Type: application/json" \
  -d '{
    "content": "Dear Jane,\n\nUpdated letter content.\n\nBest regards"
  }'

{
  "id": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
  "status": "draft",
  "recipient": "Jane Doe",
  "address": {
    "street": "Keizersgracht",
    "number": "123",
    "postalcode": "1015 CJ",
    "city": "Amsterdam",
    "country": "NL"
  },
  "content": "Dear Jane,\n\nUpdated letter content.\n\nBest regards",
  "created_at": "2026-04-14T10:00:00.000Z",
  "updated_at": "2026-04-14T10:01:00.000Z"
}

{
  "error": "Only draft letters can be updated"
}

{
  "error": "Letter not found"
}

Error codes

Status	Description
`400`	Invalid request body
`401`	Missing, invalid, or revoked API key
`404`	Letter not found or does not belong to your account
`409`	Letter is not in `draft` status

​Update a Draft

​Path parameters

​Request

​Response

​Examples

​Error codes

Update a Draft

Path parameters

Request

Response

Examples

Error codes