GAS SPONSOR (Solana): POST your transaction with our sponsor as fee payer; pay the exact fee in Solana USDC over x402; get it back co-signed.

PAID, dynamic (from $0.03 USDC, max $2.00; the 402 is the quote, issued only after a successful simulation). Body {transaction:<base64 v0 or legacy, signed by you, feePayer = the sponsor address from GET>, send?:true}. Without payment: 402 with the exact price = (network fee + priority fee + rent for token accounts it opens) x 1.3. Payment: one USDC TransferChecked of exactly amount from your token account to the sponsor's USDC account, sponsor as fee payer, signed by you, wrapped as {x402Version:2, scheme:'exact', network, accepted, payload:{transaction}} and base64d into PAYMENT-SIGNATURE (X-PAYMENT also works). The same POST then returns {transaction (co-signed), feePayer, priceUsd, lamports, feePaymentSig, settledBy, signature? when send:true, next}. Limits: sponsor only as fee payer and payer of <= 8 ATA creates; compute limit <= 1.4M units, price <= 50,000 micro-lamports/unit; 500 sponsorships per payer per day; 503 and no charge when the sponsor is low on SOL.