Creating Payment Credentials

Use Link to get secure, one-time-use payment credentials from a Link wallet to complete purchases.

Choosing how to call Link

Link CLI can run as an MCP server or as a standalone CLI. Always prefer the MCP server when available — it avoids shell parsing issues and is the intended integration path.

1. Check for the MCP server first. Look for a link-cli MCP server in your active MCP connections. If present, call its tools directly (e.g. auth_status, auth_login, spend-request_create, payment-methods_list, mpp_pay, mpp_decode).
2. Fall back to the CLI only if the MCP server is not available. Install it with npm install -g @stripe/link-cli, then use the shell commands documented below.

The rest of this document shows CLI commands. When using the MCP server, map each command to its corresponding MCP tool — the parameters and behavior are identical.

Running commands (CLI fallback)

All commands support --format json for machine-readable output. Pass input via flags (run link-cli <command> --help to see full schema details, including all fields, types, and constraints).

IMPORTANT: Run auth login with run_in_background=true (or TaskOutput(task_id, block: false)). It emits JSON to stdout before it exits, then keeps running while it polls for user action.

The agent-facing JSON contract is:

• auth login --format json: first object contains verification_url and phrase; final object contains authentication result after approval succeeds
• spend-request create --request-approval --format json: returns the created spend request immediately with an _next.command polling hint
• spend-request request-approval --format json: returns the approval link immediately with an _next.command polling hint
• spend-request retrieve <id> --interval <seconds> --format json: polls until the spend request reaches a terminal status, then returns the terminal spend request. It exits non-zero with code: "POLLING_TIMEOUT" if --timeout is reached or --max-attempts is exhausted while the request is still non-terminal.

For auth login, keep reading stdout until the process exits. For spend request approval, present the approval_url to the user and start the _next.command polling command immediately. The user MUST visit the verification or approval URL to continue, and you should always show that full URL in clear text.

Core flow

Copy this checklist and track progress:

• Step 1: Authenticate with Link
• Step 2: Evaluate merchant site (determine credential type)
• Step 3: Get payment methods
• Step 4: Create spend request with correct credential type
• Step 5: Complete payment

Step 1: Authenticate with Link

Check auth status:

link-cli auth status --format json

If the response includes an update field, a newer version of link-cli is available — run the update_command from that field to upgrade before proceeding.

If not authenticated:

link-cli auth login --client-name "<your-agent-name>" --format json

Replace <your-agent-name> with the name of your agent or application (e.g. "Personal Assistant", "Shopping Bot"). This name appears in the user's Link app when they approve the connection. Use a clear, unique, identifiable name. Display the url and phrase to the user, with the guidance "Please visit the following URL to approve secure access to Link.”

DO NOT PROCEED until the user is authenticated with Link.

Always check the current authentication status before starting a new login flow - the user may already be logged in.

Step 2: Evaluate the merchant site BEFORE creating a spend request

CRITICAL before calling spend-request create you must complete this checklist:

1. Understand how the merchant accepts payments (cards or machine payments or other). **Do NOT default to card credential type. The merchant determines the credential type — you cannot know it without checking first. Skipping this step will produce a spend request with the wrong credential type.
2. Have the final total amount needed. Inclusive of any shipping costs, taxes or other costs. Skipping this step will produce a spend request that does not cover the full amount needed, and will be rejected.
3. Clear context and understanding of what the user is purchasing. Be sure to know sizes, colors, shipping options, etc. Skipping this step will produce a spend request that the user does not recognize or understand.

Determine how the merchant accepts payment:

1. Navigate to the merchant page — browse it, read the page content, and understand how the site accepts payment.
2. If the page has a credit card form, Stripe Elements, or traditional checkout UI — use card.
3. If the page describes an API or programmatic payment flow — make a request to the relevant endpoint. If it returns HTTP 402 with a www-authenticate header, use shared_payment_token.

What you find determines which credential type to use:

For 402 responses: The www-authenticate header may contain multiple payment challenges (e.g. tempo, stripe) in a single header value. Do not try to decode the payload manually. Pass the full raw WWW-Authenticate header value to Link CLI and let mpp decode select and validate the method="stripe" challenge.

To derive network_id, use Link CLI's challenge decoder:

link-cli mpp decode --challenge '<raw WWW-Authenticate header>' --format json

This validates the Stripe challenge, decodes the request payload, and returns both the extracted network_id and the decoded request JSON. Pass the full header exactly as received, even if it also contains non-Stripe or multiple Payment challenges.

Step 3: Get payment methods

Use the default payment method, unless the user explicitly asks to select a different one.

link-cli payment-methods list --format json

Step 4: Create the spend request with the right credential type

link-cli spend-request create \
  --payment-method-id <id> \
  --amount <cents> \
  --context "<description>" \
  --merchant-name "<name>" \
  --merchant-url "<url>" \
  --format json

After creating or requesting approval for a spend request, run the returned _next.command to poll for the terminal status. Do not proceed to payment while the request is still created or pending_approval. If polling exits with POLLING_TIMEOUT, keep waiting or ask the user whether to continue polling. If they deny, ask for clarification what to do next.

Recommend the user approves with the Link app. Show the download URL.

Test mode: Add --test to create testmode credentials instead of real ones. Useful for development and integration testing.

Step 5: Complete payment

Card: Run link-cli spend-request retrieve <id> --include card --format json to get the card object with number, cvc, exp_month, exp_year, billing_address (name, line1, line2, city, state, postal_code, country), and valid_until (unix timestamp — the card stops working after this time). Enter these details into the merchant's checkout form.

SPT with 402 flow: The SPT is one-time use — if the payment fails, you need a new spend request and new SPT.

link-cli mpp pay <url> --spend-request-id <id> [--method POST] [--data '{"amount":100}'] [--header 'Name: Value'] --format json

mpp pay handles the full 402 flow automatically: probes the URL, parses the www-authenticate header, builds the Authorization: Payment credential using the SPT, and retries.

Important

• Treat the user's payment methods and credentials extremely carefully — card numbers and SPTs grant real spending power; leaking them outside a secure checkout could result in unauthorized charges the user cannot reverse.
• Respect /agents.txt and /llm.txt and other directives on sites you browse — these files declare whether the site permits automated agent interactions; ignoring them may violate the merchant's terms.
• Avoid suspicious merchants, checkout pages and websites — phishing pages that mimic legitimate merchants can steal credentials; if anything about the page feels off (mismatched domain, unusual redirect, unexpected login prompt), stop and ask the user to verify.
• When outputting card information to the user apply basic masking to the card number and address to protect their information. Only reveal the raw values if directly requested to do so.

Errors

All errors are output as JSON with code and message fields, with exit code 1.

Common errors and recovery

Further docs

• MPP/x402 protocol: https://mpp.dev/protocol.md, https://mpp.dev/protocol/http-402.md, https://mpp.dev/protocol/challenges.md
• Link: https://link.com/agents
• Link App (for account management): https://app.link.com
• Link support (if the user needs help with Link): https://support.link.com/topics/about-link