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

# Hedera's exact scheme

> The exact payment scheme for HBAR and HTS tokens, including message shapes and safety checks.

Hedera's contribution to x402 is the **`exact` scheme**, which pays a precise amount of HBAR or an HTS fungible token. It is defined in the official spec and ships with a reference TypeScript implementation.

<CardGroup cols={2}>
  <Card title="Scheme specification" icon="file-lines" href="https://github.com/x402-foundation/x402/blob/main/specs/schemes/exact/scheme_exact_hedera.md">
    `scheme_exact_hedera.md` in the x402 specs — the authoritative definition of the Hedera scheme.
  </Card>

  <Card title="Reference implementation" icon="github" href="https://github.com/x402-foundation/x402/tree/main/typescript/packages/mechanisms/hedera">
    The `@x402/hedera` package in the official x402 monorepo.
  </Card>
</CardGroup>

## Key properties

| Property         | Detail                                                                                       |
| ---------------- | -------------------------------------------------------------------------------------------- |
| Protocol version | `x402Version: 2`                                                                             |
| Networks         | `hedera:mainnet`, `hedera:testnet` (CAIP-2 identifiers)                                      |
| Assets           | Native **HBAR** (entity ID `0.0.0`) or any **HTS fungible token** (by entity ID)             |
| Amounts          | HBAR in **tinybars** (1 HBAR = 10⁸ tinybars); HTS tokens in their smallest unit per decimals |
| Fee model        | A **facilitator acts as `feePayer`**, paying network fees and submitting the transaction     |
| Transaction      | A direct, partially-signed `TransferTransaction` (no `ScheduleCreate` wrapping)              |

## The payment messages

The server advertises `PaymentRequirements`, including the facilitator's `feePayer` in `extra`:

```json PaymentRequirements theme={null}
{
  "scheme": "exact",
  "network": "hedera:mainnet",
  "amount": "1000",
  "asset": "0.0.0",
  "payTo": "0.0.1234",
  "maxTimeoutSeconds": 180,
  "extra": {
    "feePayer": "0.0.1235"
  }
}
```

The client returns a `PaymentPayload` carrying the Base64-encoded, partially-signed transaction:

```json PaymentPayload theme={null}
{
  "x402Version": 2,
  "resource": {
    "url": "https://example.com/weather",
    "description": "Access to protected content",
    "mimeType": "application/json"
  },
  "accepted": {
    "scheme": "exact",
    "network": "hedera:mainnet",
    "amount": "1000",
    "asset": "0.0.0",
    "payTo": "0.0.1234",
    "maxTimeoutSeconds": 180,
    "extra": { "feePayer": "0.0.1235" }
  },
  "payload": {
    "transaction": "AAAAAAAAAAAAA...AAAAAAAAAAAAA="
  }
}
```

After submission, the facilitator returns a settlement response:

```json SettlementResponse theme={null}
{
  "success": true,
  "transactionId": "0.0.1235@1700000000.000000000",
  "network": "hedera:mainnet",
  "payer": "0.0.1235"
}
```

<Note>
  Because the facilitator pays the fee, the spec requires it to verify that the `feePayer` is never a *net sender* of value, that net HBAR/token transfers balance to zero, that the amount credited to `payTo` matches exactly, and that the transaction has not been submitted before (replay protection). These checks protect the facilitator from being drained while sponsoring fees.
</Note>