curl --request POST \
  --url https://api.doppapp.com/v1/private/buy \
  --header 'Content-Type: application/json' \
  --header 'x-auth-token: <x-auth-token>' \
  --data '{
  "metadata": [
    {
      "client_order_id": "1234"
    }
  ],
  "orders": [
    {
      "amount": 123,
      "instrument_name": "<string>",
      "price": 123
    }
  ]
}'

{
  "tx_hash": "<string>"
}