This web site knows my account name when I visit, but still requires that I register an account to file an issue. Unnecessary and awkward when your users take the trouble to notify you of software faults.
On registration, the site could fill in my spotify account name to at least streamline the process, but does not.
Finally, as part of filing this report, since there is no label for "website" I'm forced to choose an irrelevant label. The problem is not with my Mac.
It is because the Spotify Community is hosted by a third party company, not by Spotify themselves. Your login details here will be exactly the same as for Spotify (since they operate a Single Sign On) however you get to pick your own username etc here on the community just like on other forums.