curl --request PUT \
  --url https://services.leadconnectorhq.com/contacts/{contactId}/tasks/{taskId}/completed \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --header 'Version: <version>' \
  --data '
{
  "completed": true
}
'

{
  "task": {
    "id": "lJpzYrWdpkC2hX6t2yue",
    "title": "test",
    "body": "testing",
    "assignedTo": "tesTUcmRxWrjqzJS8EjkxNKting",
    "dueDate": "2021-07-08T02:30:00.000Z",
    "completed": true,
    "contactId": "lJpzYrWdpkC2hX6t2yue"
  }
}