1👍
The reason you are getting that error is because of a mistake in your url tag usage. Your watchmovie view url definition expects an argument to be supplied for idmovie. Since you are not supplying any argument in your url tag call, it looks only for urls which do not require an argument. Since there is none, you get an error.
But that is just a symptom. The real issue is that the way you have this structured there is no view listening for a post from your form.
The easier way to structure this is to use the same view to both display the form and to play the movie. If your view is hit with a GET request, display the form. If it is hit with a POST, validate the form (which will contain the movie id) and then respond with the page that plays the movie. That way there is no need to pass idmovie within your url.. you can remove that from your url definition and also remove the need to specify the action= attribute in your tag.. it will just post right back to where it came from.