Obtain an Access Token and submit three Transactions Using Online API

I need a vb.net application that will obtain an access token and submit three test transactions using the provided documentation. I would prefer the use of RestSharp and Newtonsoft.Json references only however I am open to your suggestions. It would be a great benefit is you are used to Postman as well. This is a proof of concept application, nothing fancy needed, just 1 form with one button. I need this done within four hours.