CORS issues on real device

I’m aware that there must not be CORS issues when I run app on the real device, but it’s happening in my project.
I’ve been using ionic cordova run android command and also tried to install app manually via ADB in order to run the app only on real device, but no results so far.
To prevent possible questions - I’m not able to change backend.
I’m using ionic v4, project is built with angular v6.

try this: <access origin="*" />
add this line in your config.xml file

<content src="index.html" />
<access origin="*" />

Thanks for the suggestion, but I’ve already added this line before.
It didn’t help.