# Errors

> solana-pay-kit's error type and the boot-time safety rails that reject a bad config before the server serves traffic.

`PayKit::new` returns `Result<PayKit, PayKitError>`, so a bad configuration fails at startup rather than at request time. Per-request payment failures are turned into the `402` response by the gate — your handler only runs once a payment verifies.

## `PayKitError`

The error carries which protocol handler rejected the config:

| Variant                     | Meaning                                     |
| --------------------------- | ------------------------------------------- |
| `PayKitError::Mpp(String)`  | The MPP charge handler rejected the config. |
| `PayKitError::X402(String)` | The x402 handler rejected the config.       |

```rust
let pay = match PayKit::new(config) {
    Ok(pay) => pay,
    Err(PayKitError::Mpp(msg)) => panic!("MPP config rejected: {msg}"),
    Err(PayKitError::X402(msg)) => panic!("x402 config rejected: {msg}"),
};
```

## Boot-time safety rails

`PayKit::new` validates the config up front:

- A `challenge_binding_secret` shorter than 32 bytes (or empty) is rejected — generate one with `openssl rand -base64 32`. When it is `None`, the MPP layer reads `MPP_SECRET_KEY`.
- An unknown `network` slug is rejected; the canonical slugs are `mainnet`, `devnet`, and `localnet`.