As a newbie to HubSpot and its API, I found my worst hurdle was getting set up with a developer account and a test hub. It’s not hard once you know it, but it took me some time.
To help other .NET integrators, especially those using Microsoft ASP.NET MVC, I created a very simple walkthrough that ends up posting a contact and a company via the REST API
The walkthrough is here: https://github.com/KenCox/HubSpotMVC/wiki
Two small code snippets are in the repository here: https://github.com/KenCox/HubSpotMVC
I hope this saves someone else some aggravation.