I am a .Net developer. I work on a couple web sites that allow people to register as users / customers. This registration data is currently being synced with mailing lists at Mail Chimp. Our company is migrating from Mail Chimp to Hub Spot. I have been requested to replace the Mail Chimp sync with calls to Hub Spot to add users as they register. I am not sure yet if they will allow users to unsubscribe via our sites.
What is the fastest and easiest way to add contacts(?) to Hub Spot with data we are collecting on a C# web site?