Create a release with Octopus Client API

gistfile1.cs

var server = "http://yourserveraddress:8065/"; //Your server and IP address
var apiKey = "API-XXXXXXXXXXXXXXXXXXXXXXXXX";             // Get this from your 'profile' page in the Octopus web portal

	var endpoint = new OctopusServerEndpoint(server, apiKey);
	var repository = new OctopusRepository(endpoint);
	
	var projectId = "projects-225"; //your project id
	
	//This pulls out the info you need, the same call that's made on the Create Release page in the UI
	var template = repository.Client.Get<Octopus.Client.Model.ReleaseTemplateResource>("/api/deploymentprocesses/deploymentprocess-" + projectId + "/template");

	
	var release = new Octopus.Client.Model.ReleaseResource();
	release.Version = template.NextVersionIncrement;;
	release.ProjectId = projectId;
	foreach (var package in template.Packages)
	{
		release.SelectedPackages.Add(new Octopus.Client.Model.SelectedPackage(package.StepName, package.VersionSelectedLastRelease)); //Use a new package version if you know it
	}
			
	var result = repository.Releases.Create(release);

Try this

https://gist.github.com/mshenoy83/0ef03b990567cfe005112083ca2d2475