curl --request POST \
  --url https://api.virtuoussoftware.com/api/Contact/{contactId}/Collection/{collectionInstanceId} \
  --header 'Authorization: Bearer <token>'

{
  "customCollectionId": -51773297,
  "customCollectionName": "sint",
  "collectionInstanceId": 38041317,
  "fields": [
    {
      "name": "sit tempor in fugiat",
      "value": "sint cupidatat"
    },
    {
      "name": "officia",
      "value": "sint exercitation magna"
    }
  ]
}