Function validatePaymentRequirement

src/services/x402/client.ts:55–102

(
  requirement: PaymentRequirement,
  sessionSpentUSD: number,
)

 * Validate that a payment requirement is within configured limits.
 */
export function validatePaymentRequirement(
  requirement: PaymentRequirement,
  sessionSpentUSD: number,
): { valid: boolean; reason?: string } {
  const config = getX402Config()

  if (!config.enabled) {
    return { valid: false, reason: 'x402 payments are not enabled' }
  }

  const amountUSD = tokenAmountToUSD(requirement.maxAmountRequired)

  if (amountUSD > config.maxPaymentPerRequestUSD) {
    return {
      valid: false,
      reason: `Payment of $${amountUSD.toFixed(4)} exceeds per-request limit of $${config.maxPaymentPerRequestUSD.toFixed(2)}`,
    }
  }

  if (sessionSpentUSD + amountUSD > config.maxSessionSpendUSD) {
    return {
      valid: false,
      reason: `Payment would exceed session limit of $${config.maxSessionSpendUSD.toFixed(2)} (already spent $${sessionSpentUSD.toFixed(4)})`,
    }
  }

  // Validate network matches config
  if (requirement.network !== config.network) {
    return {
      valid: false,
      reason: `Payment requires network ${requirement.network} but wallet is configured for ${config.network}`,
    }
  }

  // Validate asset is USDC on the configured network
  const expectedAsset = USDC_ADDRESSES[requirement.network]
  if (
    expectedAsset &&
    requirement.asset.toLowerCase() !== expectedAsset.toLowerCase()
  ) {
    return {
      valid: false,
      reason: `Unknown payment token ${requirement.asset} (expected USDC: ${expectedAsset})`,
    }
  }

  return { valid: true }
}

/**
 * EIP-712 domain separator for EIP-3009 transferWithAuthorization.