> ## Documentation Index > Fetch the complete documentation index at: https://developers.fireblocks.com/llms.txt > Use this file to discover all available pages before exploring further. # x402 Troubleshooting and FAQ > Resolve common x402 issues across the Fireblocks facilitator and agent, and answers to frequent questions about cost, custody, networks, and mechanisms. Common problems and questions when running x402 on Fireblocks, covering both the [facilitator](/docs/x402-facilitator-overview) (selling) and the [agent](/docs/x402-agent) (buying). For exact message shapes and error codes, see the [Protocol Reference](/docs/x402-protocol-reference). ## Facilitator issues **The server refuses to boot, citing mainnet.** A configured asset is a mainnet asset and the testnet-only policy is in force. Use a testnet asset, or opt in deliberately with `X402_ALLOW_MAINNET=true`. The error lists the offending assets. See [Network policy](/docs/x402-facilitator-operations#network-policy). **Payments reach `settling` and never complete.** The settlement `CONTRACT_CALL` is waiting for manual approval in the Fireblocks Console. Add a Policy rule that auto-approves the `CONTRACT_CALL` from your receiver vault using the network's gas asset. See [Set Policies](/docs/set-transaction-authorization-policy). To reconcile rows that are already stuck, run `x402 payments sync ` or `x402 payments sync-all`. **An asset I imported does not appear in the `402` quote.** The asset cannot be priced. Mark stablecoins `stable: true`, or give other assets a `price_symbol`. Unpriceable assets are dropped from the response rather than rejected, so other assets stay available. See [PriceProvider](/docs/x402-facilitator-integration#priceprovider). **A payment is rejected with `unsupported_scheme`.** The resolved transfer mechanism is not in the product's pricing rows, or the request did not originate through `/api/payments/create` and is missing `extra.productId`. Offer the mechanism on the product, or route the quote through create. See [Picking a mechanism](/docs/x402-facilitator-integration#picking-a-mechanism). **A settlement failed but the funds may have moved.** Once a Fireblocks transaction ID is attached to a payment, the facilitator does not force the row to `failed` on a transient error, because the transaction may still land. Let the reconciler decide from Fireblocks's own state, or run `x402 payments sync `. See [Inspecting payments](/docs/x402-facilitator-operations#inspecting-payments). ## Agent issues **`no supported payment mechanism in accepts[]`.** The server only offered a mechanism the agent cannot sign, such as ERC-7710. Ensure the server offers `eip-3009` or `permit2`. The agent does not sign ERC-7710, because Fireblocks cannot sign delegation payloads. **`ERROR_TYPED_MESSAGE_TO_PROTECTED_7702_CONTRACT`.** A Fireblocks Policy rule blocked the signature. Add a typed-message Policy rule that allows this typed data for the agent's vault. See [Set Policies](/docs/set-transaction-authorization-policy). **`integrity check failed`.** The Payment Instruction Integrity envelope expired, the `did:web` document was unreachable, or the signature did not verify. Check the facilitator's clock skew and that the DID document is served, or relax to `VERIFY_INTEGRITY` if you are not enforcing integrity. See [Payment Instruction Integrity](/docs/x402-facilitator-operations#payment-instruction-integrity). **Payment expired.** Too much time passed between the `402` and the signed retry. Re-request to get a fresh quote, and reduce signing latency. Settlement quotes are valid for `maxTimeoutSeconds`. **Invalid signature.** The EIP-712 domain did not match. Verify the `name` and `version` in the quote's `extra`, and that the chain ID matches the asset's network. **The agent will not pay, reporting insufficient balance.** The vault is short of the spend asset. Fund it (see [Fund and Control Agent Spending](/docs/x402-agent-spending-controls)), or, only for testing, disable the check with `check_balance: false`. ## Frequently asked questions **Does my customer traffic pass through the facilitator?** No. Your server serves its own traffic and returns the `402` itself. It calls the facilitator only to verify and settle. The facilitator is API-only. **Who pays the on-chain gas?** The facilitator's vault pays settlement gas. The payer signs off-chain and spends no gas at signing time, except for a one-time setup transaction the first time it uses Permit2 or ERC-7710. **Can I accept tokens other than USDC?** Yes. USDC uses the `eip-3009` mechanism; any other ERC-20 settles through the `permit2` or `upto-permit2` mechanisms. See [Transfer mechanisms](/docs/x402-facilitator-integration#transfer-mechanisms). **Can I charge a variable amount?** Yes, with the `upto` scheme and the `upto-permit2` mechanism, where the payer signs a ceiling and the facilitator settles up to it. Your pricing logic is responsible for staying within the signed maximum. **Do I have to run the facilitator myself?** No. Fireblocks offers a managed, hosted facilitator with the same payment model. See [Get Started with x402](/docs/x402-getting-started#hosted-or-open-source-facilitator) or [talk to us about early access](https://www.fireblocks.com/#request-demo). **How do I limit what an agent can spend?** Spending limits live in Fireblocks Policy rules (per-transaction caps, velocity caps, destination allowlists, approval thresholds), not in the agent code. See [Fund and Control Agent Spending](/docs/x402-agent-spending-controls). **Is mainnet supported?** Yes, but it is off by default. The facilitator is testnet-only until you set `X402_ALLOW_MAINNET=true`. Review the operator responsibilities first. See [Network policy](/docs/x402-facilitator-operations#network-policy). ## What to read next * [x402 Protocol Reference](/docs/x402-protocol-reference) — the full error-code table and message shapes. * [x402 Quickstart](/docs/x402-quickstart) — a known-good end-to-end setup to compare against. * [Operating and Production](/docs/x402-facilitator-operations) — payment lifecycle, reconciliation, and the management API.