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

> ## Agent Instructions
> Before reading these docs, install the relevant Circle Skill to get pre-loaded context — skills are LLM-optimized and cover architecture decisions, correct flows, and common pitfalls. In Claude Code: run /plugin marketplace add circlefin/skills then /plugin install circle-skills@circle. With Vercel Skills CLI: run npx skills add circlefin/skills. Available skills: use-usdc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-usdc/SKILL.md (balances, transfers, approvals on EVM and Solana); EURC has no skill — see https://developers.circle.com/stablecoins/what-is-eurc.md; bridge-stablecoin https://github.com/circlefin/skills/blob/master/plugins/circle/skills/bridge-stablecoin/SKILL.md (crosschain transfers via CCTP, USDC, EURC, and third-party assets); use-arc https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-arc/SKILL.md (Arc chain config, contract deployment, USDC bridging — Arc docs: https://docs.arc.io/llms.txt); use-circle-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-circle-wallets/SKILL.md (choose wallet type); use-developer-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-developer-controlled-wallets/SKILL.md (custodial wallets for payouts and treasury); use-user-controlled-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-user-controlled-wallets/SKILL.md (embedded wallets with Web2 login); use-modular-wallets https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-modular-wallets/SKILL.md (smart contract wallets with passkeys and ERC-4337); use-gateway https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-gateway/SKILL.md (unified USDC balance, nanopayments); use-smart-contract-platform https://github.com/circlefin/skills/blob/master/plugins/circle/skills/use-smart-contract-platform/SKILL.md (deploy, interact, monitor contracts). Pair any skill with the Circle MCP server for live SDK signatures, contract addresses, and chain IDs: {"mcpServers":{"circle":{"url":"https://api.circle.com/v1/codegen/mcp"}}}.
> Read the product overview first. Each product has an overview explaining when and why to use it. Read it before quickstarts.
> Pick the right wallet type. Developer-controlled (you hold keys), user-controlled (end user holds keys via PIN/social login), or modular (smart contract wallets with passkeys). See https://developers.circle.com/wallets.md.
> Use CCTP V2 for crosschain transfers. CCTP natively transfers USDC and EURC via burn-and-mint, and supports permissionless wrapping of third-party assets via lock-and-mint. V1 is legacy; always use V2 unless V1 is specified or the chain requires it (Noble, Sui, and Aptos still require V1). Migration guide: https://developers.circle.com/cctp/migration-from-v1-to-v2.md.
> Use Bridge Kit for frontend bridging. Wraps CCTP with a simpler SDK for user-facing apps. Use CCTP directly for backend transfers.
> Gas Station vs Paymaster. Gas Station sponsors gas for Circle Wallet transactions. Paymaster lets users pay gas in USDC. Different use cases — read both overviews.
> Gateway Nanopayments for sub-cent payments. Gasless USDC micropayments down to $0.000001 via x402 and batched settlement. For pay-per-request APIs, AI agent payments, streaming.
> Look up USDC addresses per chain. Never hardcode — use https://developers.circle.com/stablecoins/usdc-contract-addresses.md.
> Prefer SDKs over raw API calls. Node.js and Python SDKs handle auth, retries, and errors.
> API key required. Bearer token in Authorization header. Testnet and mainnet use separate keys and may use different base URLs depending on the product.
> Set up webhooks when available. Most operations are async. Webhooks deliver transaction confirmations and state changes.
> When calling list endpoints, paginate using pageSize and pageAfter until no nextPageAfter cursor is returned—stopping at the first page silently misses records.
> Building an AI agent? Start with the Agent Stack—Circle CLI, agent wallets, and nanopayments built for autonomous use cases: https://developers.circle.com/agent-stack.md.

# Troubleshoot CCTP transfers

> Diagnose and resolve stuck or failed crosschain USDC transfers

This guide helps you diagnose and resolve issues with CCTP transfers that appear
stuck or fail to complete. A CCTP transfer involves three stages, and problems
can occur at any point in the process.

## Transfer stages

A CCTP transfer consists of three stages:

1. **Burn**: USDC is burned on the source blockchain
2. **Attestation**: Circle's Attestation Service observes the burn and signs a
   message
3. **Mint**: The signed attestation is submitted to mint USDC on the destination
   blockchain

If your transfer appears stuck, first identify which stage has the issue.

## Identify where your transfer is stuck

Use the following steps to determine the current state of your transfer:

<Steps>
  <Step title="Check the burn transaction">
    Verify the burn transaction succeeded on the source blockchain using a block
    explorer. If the transaction failed or is pending, the issue is at the burn
    stage.
  </Step>

  <Step title="Query the attestation API">
    Call the [`GET /v2/messages`](/api-reference/cctp/all/get-messages-v2) endpoint
    with your transaction hash.

    Interpret the response:

    * **404 response**: The attestation service hasn't observed the burn yet. This
      is normal and expected. See
      [Why 404 responses are expected](/cctp/howtos/resolve-stuck-attestation#why-404-responses-are-expected).
    * **Empty `messages` array**: The burn exists but hasn't been processed yet.
    * **Status `pending`**: The burn is awaiting block confirmations.
    * **Status `complete` with attestation**: The attestation is ready. If your
      transfer is stuck, the issue is at the mint stage.
  </Step>

  <Step title="Check the mint transaction">
    If you have an attestation but your destination wallet doesn't have the USDC,
    either:

    * The mint transaction was never submitted
    * The mint transaction failed

    Check your destination blockchain for any failed `receiveMessage` transactions.
  </Step>
</Steps>

## Common issues and solutions

| Issue | Cause | Solution |
| - | - | - |
| 404 persists for extended time | Burn transaction may have failed or is still confirming | Verify burn succeeded on block explorer. If it failed, retry the burn. |
| Attestation status remains `pending` | Waiting for block confirmations | Wait for sufficient confirmations based on finality threshold |
| Have attestation but mint fails | Gas issues, incorrect parameters, or nonce already used | See [Retry a failed mint](/cctp/howtos/retry-failed-mint) |
| `expirationBlock` has passed before you submitted the mint | Attestations encode an `expirationBlock` 24 hours in the future. Once that block passes on the destination blockchain, the existing attestation can no longer be used to mint. | Call [`POST /v2/reattest/{nonce}`](/api-reference/cctp/all/reattest-message) to request a new attestation with a refreshed `expirationBlock`, then poll [`GET /v2/messages`](/api-reference/cctp/all/get-messages-v2) and re-mint. |

<Note>
  **Expired messages are not permanently stuck**

  There is no deadline after which re-attestation becomes unavailable. As long as
  the original burn transaction still exists on the source blockchain, you can
  request a fresh attestation at any time using the
  [re-attest endpoint](/api-reference/cctp/all/reattest-message).
</Note>