With the arrival of macOS Mojave (10.14) applications that control other applications, as is obviously the case with SmashTunes, require permission from the user to do so. In case you've refused control and are wondering why SmashTunes isn't working properly, make sure to check the `Automation` settings within the `privacy` settings of the Security & Privacy control panel.
Unfortunately, there are no options to make this much easier (from within SmashTunes).

Security Settings

Known issues

If you've set a keyboard shortcut for "next track", and it contains the option key as modifier key, this modifier is going to be picked up by Music and used when jumping to the next track. The effect will be that instead of going to the next track, you'll be forwarded to the next album. In order to tackle this, SmashTunes will give you a second to release the option key, so you will be taken to the next track instead of the next album. So if you want to hear the next album, configure a shortcut with the option key modifier and keep it pressed for at least a second.
When querying for a tracks information, SmashTunes no longer receives the name of a track from Music. In these cases SmashTunes will display <<track title>> as a placeholder. In those cases where SmashTunes 'receives' information from Music, the correct title is sent along. This means that the information will be displayed when the next track starts. As a workaround you can pause and then resume playing the music. Let's hope Apple fixes this omission quickly.