Updates the value of one custom field on a candidate, identified by the company-level custom field ID, and returns the candidate's complete list of custom fields reflecting the change.

The submitted value is validated against the field's configured data_type: a string for string, text, or date fields; a string that must match one of the field's options.values for dropdown or radio fields; or a number for currency fields. Fields with data_type of attachment are not supported through this endpoint and return a 400 error.