Get a customer by contract id

{
  "id": 83771,
  "emailMatches": true,
  "business": false,
  "company": null,
  "firstname": "Tom",
  "lastname": "Mustermann",
  "address": "Hugo-Junkers-Str. 5",
  "phone": 49123456789,
  "email": "tom@mustermann.de",
  "tags": [
    {
      "id": 2,
      "color": "green",
      "name": "VIP"
    }
  ],
  "contracts": [
    {
      "id": 746839,
      "orderId": 123,
      "tenant": null,
      "customerId": "123",
      "signupDate": 1661126400,
      "status": "active",
      "statusCode": 5000,
      "statusCodeTitle": "active",
      "energy": "electricity",
      "energyTypeId": 1,
      "energySubTypeId": 1,
      "email": "johndoe@example.com",
      "firstname": "John",
      "lastname": "Doe",
      "deliveryAddress": "Hugo-Junkers-Str. 5, 82031 Grünwald",
      "iban": "DE89370400440532013000",
      "monthlyDeposit": 53,
      "startDate": 1661990400,
      "endDate": null,
      "consumption": 3477,
      "counterNumber": "1ESY1160669167",
      "productId": 1,
      "productName": "Flex 24",
      "productCode": "flx_24",
      "campaignId": 1
    }
  ],
  "additionalData": null
}