> ## Documentation Index
> Fetch the complete documentation index at: https://x402-stellar.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Frequently Asked Questions

> Common questions regarding fees, performance, replay protection, and networks

### What are the transaction fees on Stellar?

Transaction fees on the Stellar network are typically 100 stroops (0.00001 XLM), which equals less than \$0.00001 USD. This allows sub-cent micropayments without fees eroding revenue.

### How does replay protection work?

The `settlement-verifier` contract maintains a monotonic counter (`Nonce(Address, u64)`) in persistent storage for every payer. When a transaction is submitted, the contract enforces:
$\text{provided\_nonce} = \text{current\_nonce} + 1$
If a malicious actor intercepts and replays a signed header, the contract reverts with `Error::InvalidNonce` (code 4).

### What happens if an API request fails after payment?

In standard synchronous mode, the gateway verifies the authorization entry before forwarding. If the upstream service returns a 5xx error, the client can be issued an authorization credit or settlement can be executed optimistically via a batch relayer.

### Which networks are supported?

* `stellar:testnet`: For staging and integration testing.
* `stellar:pubnet`: Mainnet production.
* `stellar:futurenet`: For bleeding-edge protocol preview features.

### Do AI agents need lumens (XLM) to pay in USDC?

Using Soroban authorization entries (`authEntryXdr`), the agent only signs the authorization to transfer token balance. The merchant or gateway relayer submits the transaction envelope and pays the nominal fee lumens, enabling gasless agent payments.