react-native-background-download

In XCode, in the project navigator, right click Libraries ➜ Add Files to [your project's name]
Go to node_modules ➜ react-native-background-download and add RNBackgroundDownload.xcodeproj
In XCode, in the project navigator, select your project. Add libRNBackgroundDownload.a to your project's Build Phases ➜ Link Binary With Libraries
Run your project (Cmd+R)<
Open up android/app/src/main/java/[...]/MainActivity.java
Add import com.reactlibrary.RNBackgroundDownloadPackage; to the imports at the top of the file
Add new RNBackgroundDownloadPackage() to the list returned by the getPackages() method
Append the following lines to android/settings.gradle: include ':react-native-background-download' project(':react-native-background-download').projectDir = new File(rootProject.projectDir, '../node_modules/react-native-background-download/android')
Insert the following lines inside the dependencies block in android/app/build.gradle: compile project(':react-native-background-download')
In Visual Studio add the RNBackgroundDownload.sln in node_modules/react-native-background-download/windows/RNBackgroundDownload.sln folder to their solution, reference from their app.
Open up your MainPage.cs app
Add using Com.Reactlibrary.RNBackgroundDownload; to the usings at the top of the file
Add new RNBackgroundDownloadPackage() to the List<IReactPackage> returned by the Packages method