Help with installing Spotify from Software Boutique

I have just finished installing Ubuntu-Mate 18.04.1.

I tried to install Spotify from Software Boutique but it gives an error. It says:
Packages does not exist
Details:
Package spotify-client isn't available.

And says Spotify failed to install.

How to fix this?

create a file /etc/apt/sources.list.d/spotify.list with contents

deb http://repository.spotify.com stable non-free

do the usual update, then you should be able to install spotify and spotify-client

Sudo snap install spotify

Thanks. I now have installed Spotify.
But when I checked on Software Updates > Authentication, there's now 4 spotify entries. And they can't be removed.
Is it safe to just leave them be?

I also check apt-key list and it shows 4 spotify entries. 2 unknown and 2 expired. (i'm not allowed to post more than 1 image).
Is it safe to just leave them be?

Thanks.

you can remove the expired keys by taking the last 8 digits (no space), example

sudo apt-key del 48BF1C90

I don’t mind if the keys are there.

Thanks. That removed they key.