When a track title is grayed out, it means the file doesn't exist on that device. To play the track on your mobile device, you need to transfer it in one of the following ways:
■ File transfer using Mobile Library Sync
1. Connect rekordbox for Mac/Windows and rekordbox for iOS/Android to the same Wi-Fi network.
2. In rekordbox for iOS/Android, tap [Connect to rekordbox (Mac/Win)].
3. In rekordbox for Mac/Windows, click [SEARCH MOBILE].
4. Select the track from a track list in rekordbox for Mac/Windows, and right-click to show the context menu. Select [Mobile Library Sync] > [Transfer to the mobile device].
■ Using Cloud Library Sync
1. Upload the track from the device that contains it.
1-1. rekordbox for Mac/Windows: Select the track from a track list, right-click and select [Cloud Library Sync] > [Upload] from the context menu.
1-2. rekordbox for iOS/Android: Swipe the track to the left, tap [...], then tap [Upload to Cloud].
2. Once you've uploaded the track, your mobile device will display the following icon:
After swiping the track to the left, tap [...], and select [Download from Cloud].