As written above, the app needs some system grant and permissions to work correctly. The functionality of every app in the Android ecosystem is very closely tight with having the necessary right or not. If the app doesn't perform as needed, the lack of some grant might be the cause - also sometimes it could also happen,  that (especially after some Android update) some grant might be revoked by the system, the app will not notify this and the result might be e.g. black screen without any info, not working blocking etc. We have seen this behavior on some Chinese brand phones (Xiaomi, Huawei, ... but not limited to) after aggressive Android updates from manufacturer.
Well, one option then is to re-install the app, or try to check and grant those permissions manually again by opening the system list of all applications, find our application there and click on it to get the detail screen - there please scroll down to the Permissions part (mostly the route is open system Settings -> Permissions -> sometimes also Other Permissions), and check if those are there (the permission names could differ based on Android version):

  • Read Call Information (List of calls)
  • Read Contacts (Contacts)
  • Allow System Overlays (Draw over another application)
  • Phone (Use phone)

So, there are just a few permissions which must be granted to our app to keep the application running and to keep the protection fully working. Here below you will find info why we need them in detail:

Phone Contacts Permission
Your Phone Contacts helps us to determine which calls are from 'unknown' sources. We also show phone contact names instead of phone numbers in 'Logs' tab and phone number details. Without this grant the application can't distinguish between your contact and unknown number - sometimes this might cause the app will blocking all of them.

Call Info Permission
We need to know what phone number is calling to you. Without this permission our app can't work.

Set Default Phone App
This can be achieved on Android 6 sometimes with a bit of difficulties, depends on the enhancements from manufacturers - and you must then set our app to use the Active protection together with In Call Screen alert type. Android 7 and above on the other hand provides new way how to filter incoming calls, you don't have to use the In Call Screen alert type there if you don't like our dialer. It is highly recommended to set our application as default 'Phone App' to get 100% protection against unwanted calls - with this permission the app is waiting in the background and the Android itself is obliged to invoke it for every calls. See more in Which protection level should I choose?

Draw Over Other Apps
The application displays Alerts window during ringing phase. This can be done only with the 'Draw Over Other Apps' permission granted. If there is no screen with the call info, lack of this permission might be the cause. You will mostly find it in Advanced settings of your Permission system screen.

Disabling Background Optimizations
Most memory managers will try to kill any application on background if it seems not to be used actually - this will prevent our app from staying active. Disabling background optimizations for our app helps to keep the protection active. If the app is set as Default phone app with ACTIVE protection, this is not needed, but recommended. Please check these pages for more help with setting the app to stay active :

Disabling Lock Screen Optimizations (Some Devices)
Most devices terminates necessary apps every time you lock the screen. If your device has this feature, please add our application to the lock screen whitelist to keep the protection active.

If the app reports that it was disabled or not active, please check also this article: APPLICATION IS DISABLED

Depending on the functionality you need from our app, please check if all the permissions are there. If not, the app should give you a warning when you open it, but it depends also on our ability to check the permissions (which is not possible on every Android versions and especially the Android enhancements pre-built from the manufacturers). After checking this please restart (reboot) your phone. After the restart please check if our app is running and re-test the functionality.