iSunnao A7 FM Transmitter Bluetooth Radio Adapter

I bought this transmitter a few weeks ago and recently tried it out. I have a 2009 Subaru Forester with out Bluetooth, plugged this in and paired it easily. Problem is the volume, it is so low that it makes it a piece of junk to me. Maybe I am doing something wrong does anyone know anything about this? I have a iPhone 7 Plus