I have an old tablet running an old version of Android (LineageOS 12.1) and it works great for background notifications. I have a Redmi Note 7 with Android 9/LineageOS and your app and some others (AliExpress) hardly notify at all.
I have your app excluded from battery optimisation. "Problems" is not greyed out in the Settings section of your app but it does nothing when pressed now.
Not blaming you. It seems on newer versions of Android unless I actually open an app and activate it then I won't get any updates.....
