Using google speech cloud api from android give er

I am trying to build an app that use google speech cloud api in android kotlin

here is my code

launch {
             googleTextToSpeech = TextToSpeechClient.create()
             googleTextToSpeech?.let {
             viewModel.speakGoogle(googleTextToSpeech!!, totalMessage, player)
          }
       }


 fun speakGoogle(textToSpeech: com.google.cloud.texttospeech.v1.TextToSpeechClient, message: String, player: MediaPlayer) {

        val filePath = Environment.getExternalStorageDirectory().absolutePath + "/google_" + System.currentTimeMillis() + ".mp3"

        launch {

            var msg = android.text.Html.fromHtml(message).toString()
            msg = msg.replace("\"", "")


            var input = SynthesisInput.newBuilder().setText(msg).build()
            var voice = VoiceSelectionParams.newBuilder().setLanguageCode("en-US").setSsmlGender(SsmlVoiceGender.FEMALE).build()
            var audio = AudioConfig.newBuilder().setAudioEncoding(AudioEncoding.MP3).build()

            var response = textToSpeech.synthesizeSpeech(input, voice, audio)

            response?.let {

                try {
                    val inputStream = response.audioContent.toByteArray()

                    File(filePath).outputStream().use { inputStream }

                    player.setDataSource(filePath)
                    player.prepare()
                    player.start()
                } catch (e: IOException) {
                    Log.i("AMIRA00000", e.toString())
                } catch (e: IllegalStateException) {
                    Log.i("AMIRA00000", e.toString())
                }
            }
        }
    }

I am also having my google-service.json file included in the app

but I am getting the following error

java.io.IOException: The Application Default Credentials are not available. They are available if running in Google Compute Engine. Otherwise, the environment variable GOOGLE_APPLICATION_CREDENTIALS must be defined pointing to a file defining the credentials. See https://developers.google.com/accounts/docs/application-default-credentials for more information.
at com.google.auth.oauth2.DefaultCredentialsProvider.getDefaultCredentials(DefaultCredentialsProvider.java:134)
at com.google.auth.oauth2.GoogleCredentials.getApplicationDefault(GoogleCredentials.java:119)
at com.google.auth.oauth2.GoogleCredentials.getApplicationDefault(GoogleCredentials.java:91)
at com.google.api.gax.core.GoogleCredentialsProvider.getCredentials(GoogleCredentialsProvider.java:67)
at com.google.api.gax.rpc.ClientContext.create(ClientContext.java:135)
at com.google.cloud.texttospeech.v1.stub.GrpcTextToSpeechStub.create(GrpcTextToSpeechStub.java:74)
at com.google.cloud.texttospeech.v1.stub.TextToSpeechStubSettings.createStub(TextToSpeechStubSettings.java:100)
at com.google.cloud.texttospeech.v1.TextToSpeechClient.<init>(TextToSpeechClient.java:128)
at com.google.cloud.texttospeech.v1.TextToSpeechClient.create(TextToSpeechClient.java:109)
at com.google.cloud.texttospeech.v1.TextToSpeechClient.create(TextToSpeechClient.java:101)
at com.sbs16.ensofia.view.main.MainFragment$setupBinding$3$$special$$inlined$let$lambda$2.invokeSuspend(MainFragment.kt:186)
at kotlin.coroutines.jvm.internal.BaseContinuationImpl.resumeWith(ContinuationImpl.kt:33)
at kotlinx.coroutines.DispatchedTask.run(Dispatched.kt:238)
at kotlinx.coroutines.scheduling.CoroutineScheduler.runSafely(CoroutineScheduler.kt:594)
at kotlinx.coroutines.scheduling.CoroutineScheduler.access$runSafely(CoroutineScheduler.kt:60)
at kotlinx.coroutines.scheduling.CoroutineScheduler$Worker.run(CoroutineScheduler.kt:742)

I am also having another json file thathave private key and other credential settings but I do not know how to use it

I'm not an Android developer, but my feeling is that you shouldn't call the TextToSpeech directly from your Android app. You should call it through a backend (On AppEngine for example, or on Firebase Functions).

This backend is authenticated by the TextToSpeech API, and your Android client is authenticated on your backend.

Thereby, you can control who use your app, and your TextToSpeech feature. In any case, never put the service account secret key file in your app, either anybody that download you app can steal the key and perform call on the service account behalf and you will pay the bill!