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Attaches the user’s own Visa card to Agentcard so purchases charge that card directly, with no identity verification (KYC) and no balance funding needed. The tool is two-phase and conversational: the first call returns a secure link the user opens (about a minute: a one-time code from their bank plus a passkey); call attach_card again to check whether they finished. Once attached, create_card automatically mints against the attached card. If the card is not eligible (for example a business or non-US card, or an excluded issuer), fall back to create_card, which issues an Agentcard funded from the user’s cash balance.
This is the MCP counterpart of the REST card attachment flow (POST /api/v2/attach). Use REST when your backend drives the flow with a platform token; use this tool when the user’s own agent drives it over an OAuth connection.

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Parameters

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Returns

A status discriminator with a human-readable message:
  • attach_started: send the user the returned attachUrl (with expiresAt), then call attach_card again to check the result.
  • pending: the user has not finished the link yet; ask them to complete it and check again.
  • attached / already_attached: done. The connectedCardId and the card’s brand and last4 are returned, and create_card now mints against the attached card.
  • attach_ineligible: this card cannot be attached (a reason such as issuer_excluded or commercial_card says why); fall back to create_card.
  • byoc_unavailable: attaching is not available right now; fall back to create_card.
  • user_info_required: collect a phone number and terms acceptance via submit_user_info first, then call attach_card again.
With multiple cards attached, the newest active one is the default mint target; list them with list_attached_cards and pick a specific one with create_card’s connected_card_id. Unenroll one any time with remove_attached_card.

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Example

Attach a second card alongside the current one: