I've been getting this error message constantly and it's extremely aggravating. I've got a 16 GB Moto X Pure running Android 6.0 with a 32 GB memory card.
My internal storage is getting filled but there's barely anything on my SD card and the phone won't default over to it. I can only move certain apps over manually but my biggest chunk, Google Music, apparently got rid of that feature.
Is there anyway to make the phone default to the SD card as a preferred storage location?