Slack app - Trigger ID expired

Hi, so I'm testing out a Slack app from here https://github.com/soxtoby/SlackNet/blob/master/Examples/SlackNetDemo/ModalViewDemo.cs. It turns out the trigger id at line 66 expires in 3 seconds, and I'm getting the trigger id expired error, when pressing the "Open modal" modal. Any ideas to fix this? I'm just running this in a AspNet project.