garage band "Snare drum fill not an audio track"

I use Garage Band 10.3.1 and am in the middle of creating a song. I want to add a snare drum fill at the end of phrase, so I went into my loops on the far right to find an appropriate file. I chose one I liked, but when I clicked on it and dragged it onto the appropriate track, a pop-up message read "Not an audio track." I was able to drop it onto the track, but it's greyed out and when it's supposed to play, it does not.

I don't understand why it's not an audio track, but what's more I thought you could use any of those loops to enhance your songs. If not, why are they there in the first place?

Anyone have a pointer or two for me? Thanks.