In order to install Spotify with GNOME Software, launch GNOME Software,
search for Spotify and finally click the Install button.
a Linux terminal emulator,
type flatpak install nuvola eu.tiliado.NuvolaAppSpotify and press the Enter key to install this package.
You should be able to find Spotify in a list of installed applications. If not, you may have forgotten
to log out and log in and your desktop environment (Pantheon, GNOME, etc.) has not find out yet
that a new application has been installed.
Alternatively, you can launch Spotify from a terminal:
flatpak run eu.tiliado.NuvolaAppSpotify