payments

Initialize 3DS verification

Starts 3D Secure device fingerprinting for the cart’s payment method and returns the 3DS method content and the merchant transaction id for the attempt. This is the requires_3ds branch of the card payment flow (see tokenize): completing it authorizes the card and yields the Fluid payment reference the Cart checkout complete_cart step consumes as its payment_uuid query parameter (see the Checkout endpoints reference). Cart-token authenticated. Returns 404 when the cart is not found, 410 when the cart has already been processed, and 422 when 3DS is not required, not configured, already in progress, or the card is not registered.

POST

api

payments

v2026-04

carts

{cart_token}

verify

curl --request POST \
  --url https://api.fluid.app/api/payments/v2026-04/carts/{cart_token}/verify \
  --header 'Content-Type: application/json' \
  --data '{}'

{
  "tds_method_content": "PGh0bWw+Li4uPC9odG1sPg==",
  "merchant_tx_id": "018f2c1a-8b3a-7e6d-9f10-2a3b4c5d6e7f",
  "fingerprinting_required": true,
  "meta": {
    "request_id": "018f2c1a-8b3a-7e6d-9f10-2a3b4c5d6e7f",
    "timestamp": "2026-04-01T12:00:00Z"
  }
}

{
  "error_message": "<string>",
  "errors": "<string>",
  "meta": {
    "request_id": "<string>",
    "timestamp": "2023-11-07T05:31:56Z"
  }
}

{
  "error_message": "<string>",
  "errors": "<string>",
  "meta": {
    "request_id": "<string>",
    "timestamp": "2023-11-07T05:31:56Z",
    "shop_url": "<string>",
    "cart": {}
  }
}

{
  "error_message": "<string>",
  "errors": "<string>",
  "meta": {
    "request_id": "<string>",
    "timestamp": "2023-11-07T05:31:56Z"
  }
}

Path Parameters

cart_token

string

required

Opaque cart token returned by the create-cart response. It scopes the request to a single cart and is the credential for these endpoints — cart-token authentication carried in the path, with no bearer token or API key.

Body

application/json

vgs_card_id

string | null

VGS card id fallback; primarily resolved from the cart's payment method.

Response

3DS initialized

Success body for 3D Secure initialization.

tds_method_content

string | null

required

HTML content for the 3DS method (device fingerprinting) iframe.

merchant_tx_id

string

required

Merchant transaction id (UUID) issued for this 3DS attempt.

fingerprinting_required

boolean | null

required

true when the issuer requires the device-fingerprinting (3DS method) step to run in an iframe using tds_method_content before the challenge; null when not determined.

meta

object

required

Standard response metadata included on every response.

Show child attributes

Provision VGS vault credentials

Get PayPal client SDK token

curl --request POST \
  --url https://api.fluid.app/api/payments/v2026-04/carts/{cart_token}/verify \
  --header 'Content-Type: application/json' \
  --data '{}'

{
  "tds_method_content": "PGh0bWw+Li4uPC9odG1sPg==",
  "merchant_tx_id": "018f2c1a-8b3a-7e6d-9f10-2a3b4c5d6e7f",
  "fingerprinting_required": true,
  "meta": {
    "request_id": "018f2c1a-8b3a-7e6d-9f10-2a3b4c5d6e7f",
    "timestamp": "2026-04-01T12:00:00Z"
  }
}

{
  "error_message": "<string>",
  "errors": "<string>",
  "meta": {
    "request_id": "<string>",
    "timestamp": "2023-11-07T05:31:56Z"
  }
}

{
  "error_message": "<string>",
  "errors": "<string>",
  "meta": {
    "request_id": "<string>",
    "timestamp": "2023-11-07T05:31:56Z",
    "shop_url": "<string>",
    "cart": {}
  }
}

{
  "error_message": "<string>",
  "errors": "<string>",
  "meta": {
    "request_id": "<string>",
    "timestamp": "2023-11-07T05:31:56Z"
  }
}

Overview

Task guides

Endpoints

Auth endpoints

Checkout endpoints

Public SDK endpoints

Payment gateway endpoints

Cart payment endpoints

Commerce endpoints

Webhooks endpoints

Initialize 3DS verification

Path Parameters

Body

Response