curl --request PUT \
  --url https://api.virtuoussoftware.com/api/ContactIndividual/{contactIndividualId}/Collection/{customCollectionId} \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "fields": [
    {
      "name": "<string>",
      "value": "<string>"
    },
    {
      "name": "<string>",
      "value": "<string>"
    }
  ]
}
'

{
  "customCollectionId": "<integer>",
  "customCollectionName": "<string>",
  "collectionInstanceId": "<integer>",
  "fields": [
    {
      "name": "<string>",
      "value": "<string>"
    },
    {
      "name": "<string>",
      "value": "<string>"
    }
  ]
}