> ## Documentation Index
> Fetch the complete documentation index at: https://docs.4mica.io/llms.txt
> Use this file to discover all available pages before exploring further.

# Error handling

> Catch and distinguish 4Mica SDK errors, all rooted at FourMicaError.

# Error handling

All SDK errors extend `FourMicaError`. Import the specific classes to branch on failure type.

| Error                    | When it is thrown                                                                   |
| ------------------------ | ----------------------------------------------------------------------------------- |
| `ConfigError`            | Invalid `ConfigBuilder` input.                                                      |
| `RpcError`               | The 4Mica core service returned an error. Carries `.status` and `.body`.            |
| `SigningError`           | The signing scheme is unsupported, or the signer address does not match the claims. |
| `ContractError`          | An on-chain call failed or returned an unexpected result.                           |
| `VerificationError`      | A BLS certificate failed to decode or its domain did not match.                     |
| `X402Error`              | An x402 flow error: bad scheme, tab resolution, or settlement.                      |
| `AuthError`              | Base class for all authentication errors.                                           |
| `AuthMissingConfigError` | `login()` was called but auth is not configured.                                    |

The `Auth*` family also includes `AuthUrlError`, `AuthTransportError`, `AuthDecodeError`, `AuthApiError`, and `AuthConfigError`, all extending `AuthError`.

## Distinguishing errors

Import the classes you want to handle and branch with `instanceof`.

```ts theme={null}
import {
  ConfigError, // invalid ConfigBuilder input
  RpcError, // 4Mica core service error (has .status and .body)
  SigningError, // signing scheme unsupported or address mismatch
  ContractError, // on-chain call failed or unexpected result
  VerificationError, // BLS certificate decode or domain mismatch
  X402Error, // x402 flow error
  AuthError, // base class for all auth errors
  AuthMissingConfigError, // auth not configured when login() is called
} from "@4mica/sdk";

try {
  const verified = await client.recipient.verifyPaymentGuarantee(cert);
  await client.recipient.claimNetCredit(cycleId);
} catch (err) {
  if (err instanceof VerificationError) {
    // bad certificate — decode failed or domain mismatch
  } else if (err instanceof ContractError) {
    // on-chain settlement failed
  } else if (err instanceof RpcError) {
    console.error(err.status, err.body);
  }
}
```

<Note>
  Every error extends `FourMicaError`, so you can catch that base class to handle
  any SDK failure in one place.
</Note>

## Next steps

<Columns cols={2}>
  <Card title="Overview" icon="book-open" href="/sdks/typescript/overview">
    Install the SDK and see the capabilities at a glance.
  </Card>

  <Card title="Client operations" icon="wallet" href="/sdks/typescript/client-operations">
    Deposit collateral, sign payments, and settle cleared cycles.
  </Card>
</Columns>