curl --request PUT \
  --url https://virtserver.swaggerhub.com/BangoProducts/payment-provider_api/1.0.1/transaction/{transactionId} \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "userIdentifier": "987654321",
  "paymentMethods": [
    "OPERATORBILLING"
  ],
  "paymentItem": {
    "itemName": "My item",
    "itemDescription": "My item description",
    "itemCategory": "1",
    "externalPaymentItemId": "abcd-1234",
    "price": {
      "grossAmount": "3.99",
      "currencyIso3": "USD",
      "financialBreakdown": {
        "taxAmount": "0"
      }
    }
  }
}
'

const options = {
  method: 'PUT',
  headers: {Authorization: 'Bearer <token>', 'Content-Type': 'application/json'},
  body: JSON.stringify({
    userIdentifier: '987654321',
    paymentMethods: ['OPERATORBILLING'],
    paymentItem: {
      itemName: 'My item',
      itemDescription: 'My item description',
      itemCategory: '1',
      externalPaymentItemId: 'abcd-1234',
      price: {grossAmount: '3.99', currencyIso3: 'USD', financialBreakdown: {taxAmount: '0'}}
    }
  })
};

fetch('https://virtserver.swaggerhub.com/BangoProducts/payment-provider_api/1.0.1/transaction/{transactionId}', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

import requests

url = "https://virtserver.swaggerhub.com/BangoProducts/payment-provider_api/1.0.1/transaction/{transactionId}"

payload = {
    "userIdentifier": "987654321",
    "paymentMethods": ["OPERATORBILLING"],
    "paymentItem": {
        "itemName": "My item",
        "itemDescription": "My item description",
        "itemCategory": "1",
        "externalPaymentItemId": "abcd-1234",
        "price": {
            "grossAmount": "3.99",
            "currencyIso3": "USD",
            "financialBreakdown": { "taxAmount": "0" }
        }
    }
}
headers = {
    "Authorization": "Bearer <token>",
    "Content-Type": "application/json"
}

response = requests.put(url, json=payload, headers=headers)

print(response.text)