Spotify URI's are different to normal URL's and are required for a number of Spotify tools including Spotify Promo Codes.
Spotify made changes to the desktop and web apps meaning it now shows "Copy link" or "Copy embed code”.
There is a simple way to grab the URI.
On a Mac, hold down the Control or Option key and it will change from Copy Link to Copy Spotify URI.
On a PC hold down the Control or Alt key and it will change from Copy Link to Copy Spotify URI.