How do I update the Credentials after I upload a report to POWER BI

I don't believe I have Gateway Exponent or Modules. I am using Direct Query mode for my PBIX. After uploading the report to the Power BI Service I have to update the credentials.  Here is the code from the Provision example available on GITHUB: 

using (var client = await CreateClient())
{
// Get the datasources from the dataset
var datasources = await client.Datasets.GetGatewayDatasourcesAsync(workspaceCollectionName, workspaceId, datasetId);

// Reset your connection credentials
var delta = new GatewayDatasource
{
CredentialType = "Basic",
BasicCredentials = new BasicCredentials
{
Username = username,
Password = password
}
};

ExecutionReport report = null;
switch (datasources.Value.Count)
{
case 0: return new ExecutionReport(ExecutionLevel.Error, "No datasources exist to update");
case 1:
report = new ExecutionReport(ExecutionLevel.OK, "Connection credentials updated successfully.");
break;
default:
report = new ExecutionReport(ExecutionLevel.Warning, string.Format("Expected one datasource, but {0} exist, Connection credentials updated for the first", datasources.Value.Count));
break;
}

// Update the datasource with the specified credentials
await client.Gateways.PatchDatasourceAsync(workspaceCollectionName, workspaceId, datasources.Value[0].GatewayId, datasources.Value[0].Id, delta);
return report;
}

This is basically what I want to do but I don't see the PatchDatasourceAsync method in the Microsoft.PowerBI.APi.V2.Model Library. 

Here is the test code I have written to try an accomplish the update but I keep getting an internalServerError:

--I removed the two parameters from the code above becuase I dont have a Gateway setup since my data is in the azure cloud.

var credentials = AsymmetricKeyEncryptionHelper.EncodeCredentials("****", "****");

var result = PowerBIClient.Datasets.GetGatewayDatasourcesInGroupWithHttpMessagesAsync(groupid, datasetid).Result.Body.Value;

CredentialDetails cd = new CredentialDetails();
cd.Credentials = credentials;
cd.CredentialType = "Basic";
cd.EncryptedConnection = "Encrypted";
cd.EncryptionAlgorithm = "RSA-OAEP";
cd.PrivacyLevel = "Public";

UpdateDatasourceRequest udr = new UpdateDatasourceRequest(cd);

var update = PowerBIClient.Gateways.UpdateDatasourceWithHttpMessagesAsync(result.First().GatewayId, result.First().Id, udr).Result;

Thank you