What happened to You Tube Music?

A while back, I pressed the assistant button, and asked it to play a piece of music. It said, "You Tube Music must be installed to do that." So I went into Android Auto customization and activated You Tube Music, since I already pay for it monthly.

Today, I asked it to play a tune, and it said I needed to install You Tube Music to do that. I looked at the apps list, and it wasn't there. I tried to add it under customization, but it doesn't appear there either. Any ideas?