# Upsert a single custom field value on an existing shipment

Adds or updates a custom field value. The fieldKey must match a configured custom field. For numeric fields, the value must be parseable as a number. Blank values remove the field.

Endpoint: POST /integration/rest/api/v1/shipment/{shipmentExternalId}/custom-field
Version: v0
Security: X-AUTH-KEY

## Path parameters:

  - `shipmentExternalId` (string, required)
    Shipment external identifier or uuid.
    Example: "SHIP-2024-001"

## Request fields (application/json):

  - `deepLink` (string)
    Deep link URL to open this entity in Ops.App.

  - `fieldKey` (string, required)
    Unique key (name) of the custom field. This must match the configured field name.

  - `fieldValue` (string)
    Value of the custom field as a string. For numeric fields, send the number as a string.

## Response 400 fields (*/*):

  - `code` (string)
    Error code

  - `message` (string)
    Error message

  - `timeStamp` (integer)
    Timestamp

  - `correlationId` (string)
    Correlation id

## Response 403 fields (*/*):

  - `code` (string)
    Error code

  - `message` (string)
    Error message

  - `timeStamp` (integer)
    Timestamp

  - `correlationId` (string)
    Correlation id

## Response 404 fields (*/*):

  - `code` (string)
    Error code

  - `message` (string)
    Error message

  - `timeStamp` (integer)
    Timestamp

  - `correlationId` (string)
    Correlation id

## Response 500 fields (*/*):

  - `code` (string)
    Error code

  - `message` (string)
    Error message

  - `timeStamp` (integer)
    Timestamp

  - `correlationId` (string)
    Correlation id