Looking to use 2017 iPhone SE as a Volume Remote Control to 2019 iMac

Hi there BTT Community, I am brand new to BTT, and hear many great things about it. I am looking to use my 2017 iPhone SE running iOS 13.61.1 as a volume remote to control my new 2019 iMac. I have the App installed on my iPhone, but it doesn't seem to connect or show an available WIFI network in App. I also have the 45 day trial App installed on my iMac. I tried looking for documentation and haven't found any. Can anyone point me to a resource or offers some suggestions. Thanks!