Problem phones and apps
In general, Android versions that are not highly-customized work best. Google's Pixel phones, Samsung, Moto etc are all good. But there are many, many other phones models that work well with PhoneLeash.
Some phones that might cause problems are:
Oppo: Oppo phones run a special version of Android called ColorOS. ColorOS can block outgoing texts from background apps like PhoneLeash. There are settings to disable this, if you can find it!