- Make sure your SD card has at least 1GB free space and has more free space than your Android's internal cache would have if empty.
- Empty your internal cache. To do this:
- Tap Settings in the Spotify app.
- Scroll down and select Delete cache and saved data. Please note this will require you to re-sync your offline playlists.
- Tap OK. You'll be asked to confirm; click OK.
- Tap Settings in the Spotify app.
Now any offline playlists you sync will save to your SD card!
If you're having problems syncing, check the suggestions here.