1) To guarantee an exact output (e.g., exactly 6.00 USDC) on the destination chain despite bridge slippage, you cannot rely on a simple bridge quote. You must use a strategy of over-collateralization:
Calculate Input with Buffer: You request a route that bridges slightly more than the required amount (e.g., aim for 6.10 USDC).
Execute Exact Payment: On the destination chain (Base), the LI.FI Executor contract receives the 6.10 USDC (or whatever arrives after slippage). It executes your specific instruction to transfer exactly 6.00 USDC to the x402 agent.
Sweep Residue: The LI.FI Executor detects the remaining "dust" (0.10 USDC) and automatically refunds it to the user's wallet on Base in the same transaction.
2) You can use the POST /quote/contractCalls endpoint
(https://docs.li.fi/api-reference/perform-multiple-contract-calls-across-blockchains-beta)
This endpoint allows you to construct a complex destination payload.
API Flow:
Endpoint: POST https://li.quest/v1/quote/contractCalls
Key Parameters:
fromChain: 56 (BNB Chain)
fromToken: 0x... (BNB)
toChain: 8453 (Base)
toToken: 0x... (USDC Address on Base)
toAmount: Set this to the exact amount required by the x402 agent (e.g., 6000000 for 6 USDC). By setting toAmount instead of fromAmount, you trigger the reverse resolution logic in the LI.FI routing engine.
contractCalls: Array containing the specific payment logic.
3. Handling the "x402" Proof
The x402 protocol typically requires a transaction hash as proof of payment.
The Challenge: The transaction hash the user signs on BNB Chain is not the transaction hash that settles the payment on Base. They are two separate on-chain events.
The Solution: Your system must track the Lifecycle Status.
User signs tx on BNB Chain (Source Tx).
Use the LI.FI Status API (GET /status?txHash=...) to monitor the bridging.
Once the bridge completes, the Status API will provide the Receiving Transaction Hash (on Base).
This Receiving Hash is the proof your chatbot needs to present to the x402 agent to verify payment.
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