I created this hello world app like so:

1. Per the instructions here: https://capacitor.ionicframework.com/docs/getting-started/with-ionic/
   I created the app using the below commands:
   ionic start myApp tabs --capacitor
   (I chose the angular option for 'framework')
   ionic build
npx cap add android

2. Created a git repo for the project

3. Per the instructions here: https://ionicframework.com/blog/introducing-capacitor-support-for-ionic-appflow/
   I add the AppFlow feature using the below commands:
   ionic link
   (First prompt: Create new app or link existing one? I chose "create a new app")
   (Second prompt: provide a name for new app)
   (Third prompt: Link to github and selected the repository that I created in step 2, and linked to master branch)
   ionic deploy add
   (First prompt: Appflow App ID? I just clicked enter to use the created app in the previous command)
   (Second prompt: Channel Name? "Master")
   (Third Prompt: Update Method? "background")

4. I committed the code to the repo

5. I set gradlew permissions for build:
   cd android
git update-index --chmod=+x gradlew

6. Update version of gradle being used in build.gradle (root)
   classpath 'com.android.tools.build:gradle:3.6.3' (vs 3.6.1)
   A note that I chose to update this because when I built locally in android studio, it wanted to update the gradle version. I attempted an appflow build using 3.6.1 and 3.6.3 and both ended up with the error at the bottom.

7. Committed code

8. Logged into ionic appflow dashboard (https://dashboard.ionicframework.com/) and built the latest commit for android / debug

9. Downloaded apk and installed on device to verify it does not crash

10. I navigated to the project root and installed cordova-background-geolocation-lt per here: https://github.com/transistorsoft/cordova-background-geolocation-lt/blob/master/help/INSTALL_CAPACITOR.md
    I used the below commands
    npm install cordova-background-geolocation-lt
npx cap sync

11. I added the following lines to app/build.gradle

apply plugin: 'com.android.application'

+def background_geolocation = "../../node_modules/cordova-background-geolocation-lt/src/android"
+apply from: "$background_geolocation/app.gradle"

android {
    .
    .
    .
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
+           proguardFiles "$background_geolocation/proguard-rules.pro"
        }
    }
}

11. Commit to AppFlow

12. Log into ionic dashboard and built latest commit for android in debug mode

13. Build fails with:

• What went wrong: A problem occurred evaluating project ':capacitor-cordova-android-plugins'. Could not get unknown property 'applicationVariants' for object of type com.android.build.gradle.LibraryExtension.

14. Not sure if this helps, but somehow the plugin is thinking it's a release build or not recognizing capacitor correctly: