Getting a black screen instead of a QR scanner while using ML Kit to Scan Barcodes

Question

The simplest way to create a barcode scanner in Android is possibly with the Google Code Scanner API https://developers.google.com/ml-kit/vision/barcode-scanning/code-scanner

However, this doesn't seem to work for me. My code in MainActivity.kt file looks like this:

class MainActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)

        val options = GmsBarcodeScannerOptions.Builder()
            .setBarcodeFormats(
                Barcode.FORMAT_QR_CODE,
                Barcode.FORMAT_AZTEC)
            .build()

        val scanner = GmsBarcodeScanning.getClient(this, options)

        scanner.startScan()
            .addOnSuccessListener { barcode ->
                val rawValue: String? = barcode.rawValue
            }
            .addOnCanceledListener {
                // Task canceled
            }
            .addOnFailureListener { e ->
                // Task failed with an exception
            }
    }
}

The settings.gradle file has the following code:

dependencyResolutionManagement {
    repositoriesMode.set(RepositoriesMode.FAIL_ON_PROJECT_REPOS)
    repositories {
        google()
        mavenCentral()
    }
}

My build.gradle file has the following dependency:

implementation 'com.google.android.gms:play-services-code-scanner:16.0.0'

I have added the following to my AndroidManifest.xml file:

<meta-data
            android:name="com.google.mlkit.vision.DEPENDENCIES"
            android:value="barcode_ui"/>

However, I only get a black screen while running the app. The Google QR code scanner UI is showing up but the camera doesn't seem to work. The entire screen is black.

Update:

The app works on one device but not the other. What could be wrong here?

Thanks.