I have a template with a form in it. the action is a url ( /user/display ).

I also have a route handler  /user/display

But when I submit the form, the url on the website change to /user/display  , but the browser cannot display it. 'This webpage is not available'. The log file says 

looking for /user/display/index

 But when I reload the page, it works as expected.

Any ideas why when first time to load the page, it doesn't work, there is /user/display route, why it is looking for /user/display/index which doesn't exist?

Many thanks,

Dan