Google Play Music downloaded music not storing on SD card

I have a Motorola Moto G3 with a measly 4GB of storage, so I bought a 32GB SD card. I installed it as **internal** storage. I have a subscription to Google Play Music and spend a lot of time without an internet connection, so I download a lot of music. I set GPM's storage location to the SD card, but when I try to install apps, it says I'm out of storage even though there's plenty of space left on the SD card. I took a look at the storage and GPM is using practically all the internal storage. I'm also confused because the SD card shows different amounts used in different menus. I need to either get GPM to store on the SD card like it should or get apps to install anyway. I guess apps can't install if you don't have internal storage free?