---
title: "Add existing contacts to a list (by id)"
method: POST
path: "/business/lists/{listId}/members"
tags: ["Lists"]
---

# Add existing contacts to a list (by id)

`POST /business/lists/{listId}/members`

## Request

- Base URL: `https://api.tryfuse.ai/api/v1`
- URL: `https://api.tryfuse.ai/api/v1/business/lists/{listId}/members`
- Auth: HTTP basic

Adds existing contacts to the list by id (row ids from `GET /business/lists/{listId}/rows` on another list, or `POST /business/contacts/resolve`). Idempotent: contacts already in the list are skipped, so `addedCount` (net new members) can be lower than `submittedCount`. Up to 5,000 ids per call; no credits are spent.

Errors:
- `404` `LIST_NOT_FOUND` — No list with that id is visible to the token owner.
- `422` `VALIDATION_FAILED` — contactIds missing, empty, over 5000 entries, or containing a non-24-hex id.
- `429` `RATE_LIMITED` — The lists rate bucket is exhausted.

Requires one of the following token scopes: lists.

## Path parameters

- `listId` string, required: 24-character hex id of the list (from GET /business/lists).

## Request body

- object
  - `contactIds` string[], required: Contact ids (24-character hex, 1-5000 per call) to add to or remove from the list; ids already in the list are ignored on add.

## Response `200`

Success

- object
  - `submittedCount` integer, required
  - `addedCount` integer, required

## Other responses

- `400`: Error
- `401`: Error
- `402`: Error
- `403`: Error
- `404`: Error
- `409`: Error
- `422`: Error
- `429`: Error
- `500`: Error

---

[API](https://skmtc.dev/fuseai/apis/fuse-business-api.md) · [All operations](https://skmtc.dev/fuseai/apis/fuse-business-api/llms.txt) · [OpenAPI document](https://skmtc.dev/fuseai/apis/fuse-business-api/revisions/50d95e0536f4?raw)