Second Opinion
The five-minute funding guide

Put $5 where your agent can spend it

Every paid call here costs cents in USDC over x402 (quick 2¢ · verify 20¢ · panel 75¢) — $5 buys ~250 quick checks. The wallet is the account: no signup, no API key, just a funded address whose key stays on your machine. This page exists because the two failure modes we actually observe are both funding failures: wallets created on the wrong network, and wallets that quietly run dry mid-pipeline.

No wallet at all yet? You don't need one to evaluate: POST /v1/try (or the npm/PyPI clients' freeTry) serves the identical quick engine free, rate-limited, no payment. Fund a wallet when you're ready for signed verdicts and real allowances.

What each rail actually needs

RailThe wallet needsExchange withdrawal network nameGotchas
BaseUSDC only — never any ETH (the facilitator submits and pays gas)"Base"None. The easiest rail.
PolygonUSDC only — no POL/MATIC needed"Polygon" (sometimes "Polygon PoS")Pick plain USDC, not "USDC.e" — the bridged variant cannot authorize x402 payments. Native contract: 0x3c499c542cEF5E3811e1192ce70d8cC03d5c3359
AlgorandUSDC (asset 31566704) + ~0.3 ALGO minimum balance"Algorand"The wallet must opt in to the USDC asset once before it can receive it (one click in Pera/Defly; exchanges handle it on their side, your receiving wallet doesn't get it automatically).
SolanaUSDC + ~0.01 SOL for rent"Solana"Use the /async routes (pay, get a job id, poll free) — Solana transactions expire in ~60s, too short for a long sync call.

One EVM key is one address on Base and Polygon — fund whichever chain, same wallet. Balances never pool across chains, though: $1 on Polygon is not spendable on Base.

The five minutes, step by step

  1. Make a throwaway wallet for the agent. Don't reuse a personal wallet: generate a fresh key (any wallet app, or programmatically), give the agent the key via env var, and treat the balance like cash in a pocket — a few dollars, not a treasury.
  2. Buy USDC on any major exchange (Coinbase, Kraken, etc.) — $5–10 is plenty to start.
  3. Withdraw to the agent's address, choosing the network from the table above. The network dropdown decides which chain the money lands on; fees on these networks are pennies.
  4. Point the client at the key — e.g. SECOND_OPINION_PRIVATE_KEY for Base/Polygon in the npm / PyPI clients — and make a 2¢ call. The payment signs locally; the key never leaves your process.

Keep it funded (learn from the wallet that died)

Our first production customer was an autonomous pipeline that ran perfectly for three days, spent its balance to zero across several x402 services, and went dark mid-schedule. Build against that: check the balance in your loop (a free RPC call), alert yourself below ~50 checks of runway, and handle a payment rejection gracefully — our 402 responses tell you exactly what happened in plain JSON, and while the free trial is enabled they include a free_fallback pointer so a monitoring loop can degrade instead of dying. Working code for that pattern: /recipes, pattern 4.