Below is part of my .spec file:
--------------------------------------------------

%install
install -Dm644 mattermost.service %{buildroot}/usr/lib/systemd/system/mattermost.service
install -Dm644 mattermost-user.conf %{buildroot}/usr/lib/sysusers.d/mattermost.conf

%files
%{_libdir}/systemd/system/mattermost.conf
%{_libdir}/sysusers.d/mattermost.conf

----------------------------------------------

which throw two errors when building:

error: File not found: /home/makerpm/rpmbuild/BUILDROOT/mattermost-3.4-1.fc24.x86_64/usr/lib64/systemd/system/mattermost.conf
error: File not found: /home/makerpm/rpmbuild/BUILDROOT/mattermost-3.4-1.fc24.x86_64/usr/lib64/sysusers.d/mattermost.conf

I understand I installed these two files in /usr/lib/ (which is what I want), as said by the below output:
----------------------------------------------------------
+ install -Dm644 mattermost.service /home/makerpm/rpmbuild/BUILDROOT/mattermost-3.4-1.fc24.x86_64/usr/lib/systemd/system/mattermost.service
+ install -Dm644 mattermost-user.conf /home/makerpm/rpmbuild/BUILDROOT/mattermost-3.4-1.fc24.x86_64/usr/lib/sysusers.d/mattermost.conf
----------------------------------------------------------

BUT Fedora is looking for them in /usr/lib64, right ?

So %{_libdir} seems to point to /usr/lib64 rather than to /usr/lib as mentioned in wiki[0].

Am I right? Shall I then write this in %files ? :

/usr/lib/systemd/system/mattermost.conf
/usr/lib/sysusers.d/mattermost.conf

Thank you for help.

[0]https://fedoraproject.org/wiki/How_to_create_an_RPM_package