FuelSDK no longer returns data from API integration after client created new Salesforce account

Question

I have a client who recently had to create a new Salesforce account and needed their API integration updated. The API calls that were built before I took over just send over the client id and the client secret. I've noticed some subtle differences between their two accounts, but I'm unsure what has changed on the back end for Salesforce that would prevent the FuelSDK from talking to the API. I've talked to a help desk person from Salesforce but they didn't have any experience dealing with the API or FuelSDK directly and couldn't give any advice on how to proceed. My initial impression is that the FuelSDK that's being used in my clients code needs to be updated, but before I go that route I thought it would pose this question here.

    private static ET_Client GetClient(string clientId, string clientSecret)
    {
        var parameters = new NameValueCollection();
        parameters.Add("clientId", clientId);
        parameters.Add("clientSecret", clientSecret);
        return new ET_Client(parameters);
    }

Answer 1

It looks like the client was using the legacy API package. There is a V2 that has different parameter/naming convention in order to get a token. V2 Access Token