Does Dropbox remove trailing slash at the end of an url?

It looks like you're referring to the step where Dropbox redirects the user back to the URI you specify in the redirect_uri parameter you set on /oauth2/authorize. 

I just checked on this, and it does not appear Dropbox itself is removing the trailing "/" from that URL. I reproduced this, and looking at the log of the network requests, I see that Dropbox is redirecting the user to the supplied redirect URL including the trailing "/", and then your server is itself returning another redirect to a URL without the trailing "/". Please see the attached screenshots:

If you don't want the trailing "/" removed, you'll need to update your server's code to remove that behavior. That's out of our control as that would be in your code, so I can't offer help on the specifics for doing so.