> ## 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.

# User-controlled wallet SDK error codes

> Error codes surfaced by the user-controlled wallet SDK's built-in UI.

For error codes returned by the Wallets API, see
[Wallets API error codes](/api-reference/wallets/error-codes).

| Error code | Error message | Resolution |
| - | - | - |
| `155701` | `User canceled` | No action required. |
| `155702` | `(UI launch failure message varies)` | Check the error message for the exact UI launch failure reason. |
| `155703` | `The code you entered is not the same as the first one` | Prompt the user to re-enter the confirmation code so it matches the first entry. |
| `155704` | `Your PIN can't have repeating or consecutive numbers` | Prompt the user for a PIN without repeating or consecutive numbers. |
| `155705` | `Your hint can't be the same as the answer` | Prompt the user for a hint that differs from the answer. |
| `155706` | `Network error` | Retry the request. |
| `155707` | `Failed to encrypt data` | Retry the request. |
| `155708` | `"Biometrics instead of PIN" is disabled` | Enable "Biometrics instead of PIN" via the SDK. |
| `155709` | `The device system doesn't support biometrics` | Fall back to PIN authentication. |
| `155710` | `Failed to decrypt biometrics key` | Prompt the user to reset biometrics on the device. |
| `155711` | `The user has not enabled biometrics yet` | Prompt the user to enable biometrics if the flow requires it. |
| `155712` | `The user refused to enable biometrics` | Call the `SetBiometricsPin` SDK API so the user can enable biometrics. |
| `155713` | `Too many requests. Try again later` | Wait 30 minutes before retrying. |
| `155714` | `Too many requests. The biometrics sensor on the device is locked` | Prompt the user to unlock biometrics in device settings. |
| `155715` | `The user didn't enable biometrics` | Prompt the user to re-allow biometrics in App Settings. Doing so relaunches the app. |
| `155716` | `Unexpected error for biometrics` | Retry the request. |
| `155717` | `User secret is missing. Check the input parameters.` | Include the user secret in the request. |
| `155718` | `User token format is invalid` | Log the user in again to get a valid token, then re-execute the challenge. |
| `155719` | `User token and SDK API execute function do not match. Please ensure that executeWithUserSecret is for users with SSO/Email auth method, and execute is for users with PIN auth method.` | Use `executeWithUserSecret` for the SSO or email auth method, and `execute` for the PIN auth method. |
| `155720` | `Social login failed` | Check the error message from the social provider for details. |
| `155721` | `Login info is missing` | Log the user in and re-execute the challenge. |