When I click View, error "that page cannot be found"

= I am getting a 404 when I add a new route =

You need to go to Settings > Permalinks and click “save”. This flushes the WordPress rewrite rules. For performance reasons, the rewrite rules are only flushed either when the plugin is activated or when the Permalinks are saved. So, if you are developing with the plugin activated and adding controller routes as you go, you need to use this approach to flush the rewrite rules and use your new URL endpoints.