I doubt that you have to add a request handler manually, I think the deeplink module takes care of this. All you need to do is add microflow DeepLink.Startdeeplink to your mendix startup microflow.
This will register the request handler.
Next you need to configure some deeplinks. To do this you need to access the page DeepLink.DeepLinkConfigurationOverview. Best to add this page as a navigation item for your admin role. Then follow the instructions on how to configure a deeplink, I think the minimum you need is a name and a microflow.
Hope this helps,
PS: Just to clarify, you need to add the page-DeepLink.DeepLinkConfigurationOverview to your navigation in the modeler, then start the application and go to this page, and here in the browser you can configure the deeplinks.
Thank you for the answer. It helped.