For 16.0 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:maxiotis:Testing/16.0/home:maxiotis:Testing.repo
zypper refresh
zypper install spotify-client
For 15.6 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:maxiotis:Testing/15.6/home:maxiotis:Testing.repo
zypper refresh
zypper install spotify-client
For 15.5 run the following as root:
zypper addrepo https://download.opensuse.org/repositories/home:maxiotis:Testing/15.5/home:maxiotis:Testing.repo
zypper refresh
zypper install spotify-client