{
  "requestId": "...",
  "success": false,
  "error": {
    "code": 1001,
    "key": "VALIDATION_FAILED",
    "message": "Invalid request data"
  }
}

const response = await fetch('https://api.assetpay.co/client/trading/deposit', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'Authorization': clientToken
  },
  body: JSON.stringify(depositPayload)
});

const result = await response.json();

if (!result.success) {
  switch (result.error.key) {
    case 'PRICE_CHANGED':
      // Refetch inventory and show updated prices
      break;
    case 'ITEMS_UNAVAILABLE':
      // Remove unavailable items from selection
      break;
    case 'DEPOSIT_IN_PROGRESS':
      // Tell user to wait for current deposit to finish
      break;
    case 'MERCHANT_BALANCE_LOW':
      // Withdrawal can't proceed, notify user
      break;
    default:
      // Log the error for debugging
      console.error(`Trade error: ${result.error.key} (${result.error.code})`);
  }
}