On the page:
https://developer.chrome.com/multidevice/android/customtabs

The section about "Add your app as the referrer" has code for adding a referrer URI. But by using the code, the URI becomes "2://com.example.app" as the const Intent.URI_ANDROID_APP_SCHEME is an integer flag that is designed to be used by Intent.parseUri and not as a string.

So the code example should be changed to:
intent.putExtra(Intent.EXTRA_REFERRER, 
        Uri.parse("android-app://" + context.getPackageName()));