> ## Documentation Index
> Fetch the complete documentation index at: https://docs.agentcard.sh/llms.txt
> Use this file to discover all available pages before exploring further.

# Attach a card

> Let a user share their own bank card so their agent's purchases charge it directly — the fastest integration path.

The attach flow lets a user share a real bank card with their agent. Once the
card is attached, every single-use card the agent creates charges the user's
own card directly — no identity verification (KYC) and no balance to fund.
That makes this the fastest path to production: if your users already have an
eligible card in their pocket, there is nothing else to collect.

Eligible cards are **US-issued consumer Visa** cards and consumer
**Mastercard** cards from any country. Multi-use cards are the one exception
to this path — they stay balance-funded, so they need the
[create card flow](/companies/guides/create-card-overview) instead.

## The flow you implement

Three steps, in order. Each page contains a paste-ready instruction block for
your coding agent plus the underlying API calls.

<Steps>
  <Step title="User authentication">
    Connect the user to Agentcard from inside your own app. Your backend
    triggers a one-time code and receives the user's `user_id` and connection
    tokens — no redirects, no hosted sign-in page.
    [Implement user authentication →](/companies/api/user-authentication)
  </Step>

  <Step title="Card attachment">
    Your backend asks Agentcard for a secure link; the user opens it and adds
    their card in about a minute (a one-time code from their bank plus a
    passkey). The card number is entered on the hosted page only — it never
    touches your servers.
    [Implement card attachment →](/companies/guides/attach-card)
  </Step>

  <Step title="MCP server">
    Point your agent at the Agentcard MCP server with the user's connection
    token. The card tools load automatically — the agent creates single-use
    cards against the attached card with `connected_card_id`.
    [Wire up the MCP server →](/companies/guides/mcp-server)
  </Step>
</Steps>

## When to use which flow

Use **attach** when your users can pay with a card they already have — it
skips KYC and wallet funding entirely. Use
[create card](/companies/guides/create-card-overview) when you need
balance-funded cards (multi-use cards, spend controlled by a prepaid balance)
or when the user's card isn't eligible: an ineligible attach returns
`attach_ineligible`, and the agent can switch flows by calling `create_card` —
which may first require KYC and wallet funding.

Everything works in test mode first — see
[Testing cards in staging](/companies/testing) for eligible test card numbers.