[SCDOLAB]

This adds a short "Paying into a contract address" section to examples/base-mainnet/README.md. It covers a question I had while setting up the gateway: can MERCHANT_WALLET be a contract, such as a revenue-split contract on Base, rather than an EOA?

What I checked:

• With MERCHANT_WALLET set to a Base contract address, validate passes on examples/base-mainnet/config.yaml.
• In the code, the merchant address is used only as payTo (settle.ts payee). Nothing signs with it, and the only check is the Anvil dev-address guard.

Not tested: a live mainnet settlement through this gateway. I don't have CDP credentials. I tried examples/base-mainnet-payai, but start crashed my box with a segfault, because its better-sqlite3 native build failed there (no make). That's my environment, not the gateway. The USDC behaviour itself (transferWithAuthorization to a contract to) is standard EIP-3009 and doesn't call the recipient.

The change is docs only. I'm happy to reword it or move it to docs/configuration.md.

[Revinand]

Thanks for this and for listing what you checked and what you could not test.

The claim holds: the gateway uses payTo only as the destination and never checks whether it has code. I also ran the settlement you could not: on a local Anvil chain, a payment through the gateway and the x402 SDK client to a deployed contract settled and the contract received exactly the price. It used MockUSDC, so it says nothing about CDP's facilitator.

Before I merge:

1. Add a cross-chain caveat. A contract exists only on the chain where it was deployed, while an EOA's key controls its address on every EVM chain. docs/configuration.md reuses ${MERCHANT_WALLET} for Base and Polygon offers. Setting it to a Base contract would send Polygon payments to an address nobody controls there.
2. Drop the first caveat. MERCHANT_WALLET is never used as a key or signer.
3. Style: pad the edited table row (npx prettier --write) and avoid contractions, as the other docs do.

Suggested section:

## Paying into a contract address
 
`MERCHANT_WALLET` sets the x402 `payTo` address, which can be a contract such as a revenue splitter on Base. USDC's EIP-3009 `transferWithAuthorization` transfers tokens without invoking a recipient callback, so the contract needs no receive handler.

Before using a contract:
- Confirm it can send USDC onward, for example through its `distribute` function. Otherwise, the funds stay at that address.
- Verify its deployment on each offer's network. Do not reuse the address on another network unless the intended contract is also deployed there.

Moving the general rule to docs/configuration.md, with a pointer here, is also fine. I will squash-merge as docs: note that a contract can receive x402 payments.