Account Transfers (ACATS)

An ACATS transfer moves a customer’s holdings from another US broker-dealer into their Buildmarkets account through the NSCC’s Automated Customer Account Transfer Service. Use it when a customer already holds positions elsewhere and wants to consolidate them with you, rather than selling and re-buying. Buildmarkets supports incoming, full-account transfers:

Incoming — assets are pulled into a Buildmarkets account from the delivering firm.
Full — the whole account moves, and the account at the delivering firm is closed.

ACATS transfers are only supported on self-directed accounts. Initiating a transfer on a managed account returns 400 ACAT_NOT_ALLOWED_FOR_MANAGED.

Endpoints

Method	Path	Description	Scope
`GET`	`/v1/acats/brokers`	List common delivering broker-dealers and their DTC numbers	`accounts:read`
`POST`	`/v1/accounts/{accountId}/acats/incoming`	Initiate an incoming transfer	`accounts:write`
`GET`	`/v1/accounts/{accountId}/acats`	List transfers for an account	`accounts:read`
`GET`	`/v1/accounts/{accountId}/acats/{acatId}`	Get a single transfer	`accounts:read`

Transfer lifecycle

      POST .../acats/incoming
               │
        ┌──────▼──────┐
        │   pending   │  ◄─── Submitted; awaiting the delivering firm
        └──────┬──────┘
               │
        ┌──────▼──────┐
        │  submitted  │  ◄─── Accepted by NSCC; in the delivering firm's queue
        └──────┬──────┘
               │
          ┌────┴────┐
          │         │
    ┌─────▼───┐ ┌───▼──────┐
    │ settled │ │ rejected │  ◄─── The transfer could not be completed
    └─────────┘ └──────────┘

Status	Meaning
`pending`	The transfer has been submitted and is awaiting acknowledgement from the delivering firm
`submitted`	NSCC has accepted the request and it is in the delivering firm’s queue
`settled`	Assets have been re-registered to the Buildmarkets account
`rejected`	The transfer did not complete

There are no webhook events for ACATS transfers. Poll GET /v1/accounts/{accountId}/acats/{acatId} to track progress.

1. Choose the delivering firm

The transfer needs the delivering firm’s DTC/NSCC participant number. GET /v1/acats/brokers returns common firms so you can build a picker in your UI.

curl https://dev-tapp-api.tappengine.com/v1/acats/brokers \
  -H "X-API-Key: YOUR_API_KEY" -H "X-API-Secret: YOUR_API_SECRET"

{
  "brokers": [
    {
      "code": "schwab",
      "name": "Charles Schwab",
      "dtc_number": "0164",
      "logo_url": null
    }
  ]
}

Field	Type	Description
`code`	string	Stable identifier for the firm. Use this in UI logic rather than matching on `name`
`name`	string	Display name
`dtc_number`	string	DTC/NSCC participant number — pass this as `contra_broker_dealer_number`
`logo_url`	string \| null	Logo for display, if available

This list is a convenience, not an allowlist. The initiate endpoint accepts any valid DTC number, so let customers enter one manually if their firm is not listed.

2. Initiate the transfer

POST /v1/accounts/{accountId}/acats/incoming

Field	Type	Required	Description
`contra_broker_dealer_number`	string	✅	DTC/NSCC number of the delivering firm
`contra_account_number`	string	✅	The customer’s account number at the delivering firm
`account_holder_name`	string		Registered account name at the delivering firm. Used by NSCC to match the account
`tax_id`	string		SSN or EIN on the account at the delivering firm. Used by NSCC to match the account, and never returned in any response

curl -X POST https://dev-tapp-api.tappengine.com/v1/accounts/ACCOUNT_ID/acats/incoming \
  -H "X-API-Key: YOUR_API_KEY" -H "X-API-Secret: YOUR_API_SECRET" \
  -H "Content-Type: application/json" \
  -d '{
    "contra_broker_dealer_number": "0164",
    "contra_account_number": "12345678",
    "account_holder_name": "Jane Doe"
  }'

Supplying account_holder_name and tax_id exactly as they appear at the delivering firm reduces the chance of a rejection for mismatched details.

Response (201 Created):

{
  "id": "7c1e9a42-3b5d-4f8e-a6c2-9d0b1e2f3a4c",
  "account_id": "b3f2c9a1-7d4e-4f8a-9c1b-2e3d4f5a6b7c",
  "direction": "incoming",
  "transfer_type": "FUL",
  "status": "pending",
  "contra_broker_dealer_number": "0164",
  "contra_account_number": "12345678",
  "assets": [],
  "created_at": "2026-09-15T14:32:00Z",
  "updated_at": "2026-09-15T14:32:00Z"
}

Field	Type	Description
`id`	string	Transfer identifier. Stable for the life of the transfer — pass it to `GET .../acats/{acatId}`. Treat it as an opaque string: its format is not guaranteed to be a UUID
`account_id`	string (UUID)	The receiving Buildmarkets account
`direction`	string	Always `incoming`
`transfer_type`	string	Always `FUL` (full transfer)
`status`	string	`pending`, `submitted`, `settled`, or `rejected`
`contra_broker_dealer_number`	string	DTC/NSCC number of the delivering firm
`contra_account_number`	string	The customer’s account number at the delivering firm
`assets`	array	Positions included in the transfer, each with `symbol`, `quantity`, and `asset_category`
`created_at`	string (ISO 8601)	When the transfer was initiated
`updated_at`	string (ISO 8601)	When the transfer was last updated

3. Track the transfer

List every incoming transfer on an account:

curl https://dev-tapp-api.tappengine.com/v1/accounts/ACCOUNT_ID/acats \
  -H "X-API-Key: YOUR_API_KEY" -H "X-API-Secret: YOUR_API_SECRET"

{
  "transfers": [
    {
      "id": "7c1e9a42-3b5d-4f8e-a6c2-9d0b1e2f3a4c",
      "account_id": "b3f2c9a1-7d4e-4f8a-9c1b-2e3d4f5a6b7c",
      "direction": "incoming",
      "transfer_type": "FUL",
      "status": "submitted",
      "contra_broker_dealer_number": "0164",
      "contra_account_number": "12345678",
      "assets": [],
      "created_at": "2026-09-15T14:32:00Z",
      "updated_at": "2026-09-15T14:33:10Z"
    }
  ]
}

Or fetch one transfer by its id:

curl https://dev-tapp-api.tappengine.com/v1/accounts/ACCOUNT_ID/acats/7c1e9a42-3b5d-4f8e-a6c2-9d0b1e2f3a4c \
  -H "X-API-Key: YOUR_API_KEY" -H "X-API-Secret: YOUR_API_SECRET"

The response has the same shape as the 201 response above.

Testing in sandbox

In sandbox, a transfer’s status advances automatically based on how long ago it was created, so you can build and test your polling loop without waiting on real settlement:

Time since creation	Status
0–30 seconds	`pending`
30 seconds – 2 minutes	`submitted`
After 2 minutes	`settled`

Sandbox transfers always settle. To test your handling of rejected, simulate that state in your own code.

Common errors

HTTP Status	Error	Cause
`400`	`MISSING_FIELDS`	`contra_broker_dealer_number` or `contra_account_number` is missing
`400`	`ACAT_NOT_ALLOWED_FOR_MANAGED`	The account is a managed account. ACATS transfers are only supported on self-directed accounts
`403`	`FORBIDDEN`	The API key lacks the required scope
`404`	`ACCOUNT_NOT_FOUND`	The `accountId` does not exist or is not accessible to your partner
`404`	`ACAT_TRANSFER_NOT_FOUND`	No incoming transfer with that `acatId` exists on this account

Next steps

Deposits & Withdrawals → — Move cash in and out of the account
Positions & Portfolio → — View the positions once a transfer settles

Self-Directed Investing

Platform Operations

Account Transfers (ACATS)

Endpoints

Transfer lifecycle

1. Choose the delivering firm

2. Initiate the transfer

3. Track the transfer

Testing in sandbox

Common errors

Next steps

​Endpoints

​Transfer lifecycle

​1. Choose the delivering firm

​2. Initiate the transfer

​3. Track the transfer

​Testing in sandbox

​Common errors

​Next steps

Endpoints

Transfer lifecycle

1. Choose the delivering firm

2. Initiate the transfer

3. Track the transfer

Testing in sandbox

Common errors

Next steps