curl --request GET \
  --url http://localhost:4000/v1/transactions/sign/{transactionId} \
  --header 'Authorization: <api-key>'

{
  "success": true,
  "message": "<string>",
  "data": {
    "transactionId": "tx-uuid-abc123",
    "signedTransaction": "0x...",
    "status": "pending",
    "from": "0x123...",
    "to": "0x456...",
    "amount": "1.5",
    "chainId": 43114,
    "tokenAddress": "0x...",
    "expiresAt": "2024-01-01T12:15:00Z",
    "createdAt": "2024-01-01T12:00:00Z"
  },
  "statusCode": 123,
  "timestamp": "<string>",
  "path": "<string>"
}