---
title: "Create a supplemental document for an Entity"
method: POST
path: "/entity_supplemental_documents"
---

# Create a supplemental document for an Entity

`POST /entity_supplemental_documents`

## Request body

- CreateASupplementalDocumentForAnEntityParameters
  - `entity_id` string, required — The identifier of the Entity to associate with the supplemental document.
  - `file_id` string, required — The identifier of the File containing the document.

## Response `200`

Supplemental Document

- EntitySupplementalDocument — Supplemental Documents are uploaded files connected to an Entity during onboarding.
  - `created_at` string, date-time, required — The [ISO 8601](https://en.wikipedia.org/wiki/ISO_8601) time at which the Supplemental Document was created.
  - `entity_id` string, required — The Entity the supplemental document is attached to.
  - `file_id` string, required — The File containing the document.
  - `idempotency_key` string, nullable, required — The idempotency key you chose for this object. This value is unique across Increase and is used to ensure that a request is only processed once. Learn more about [idempotency](https://increase.com/documentation/idempotency-keys).
  - `type` 'entity_supplemental_document', required — A constant representing the object's type. For this resource it will always be `entity_supplemental_document`.

## Other responses

- `4XX` — Error
- `5XX` — Error

---

[API](https://skmtc.net/increase/apis/increase-api.md) · [All operations](https://skmtc.net/increase/apis/increase-api/llms.txt) · [OpenAPI document](https://skmtc-service-staging.skmtc.workers.dev/v1/apis/increase/increase-api/versions/22125d715935/schema)