curl --request POST \
  --url https://openapi.enginy.ai/v1/add-contact-group-to-campaign \
  --header 'Content-Type: application/json' \
  --header 'x-api-key: <api-key>' \
  --data '
{
  "campaignId": 123,
  "contactGroupId": 123
}
'

{
  "message": "<string>",
  "data": {
    "requestedCount": 123,
    "addedCount": 123,
    "reactivatedCount": 123,
    "alreadyInCampaignCount": 123,
    "skippedDeletedConversationCount": 123,
    "skippedContactIds": [
      123
    ],
    "campaignStatus": "<string>",
    "campaignAppUrl": "<string>"
  }
}