@klm113 This has something to do with browser caching and your redirect. The above redirect('/show') issues out a 302 temporary redirect request.
To fix the above, specifically specify where by using the redirect()->to('/show') which should issue out a 303 response informing the browser that it is done with the post request and can now proceed to the /show route.
checkout this video here for more: Prevent duplicate form submissions using the Post / Redirect / Get pattern