How to send a .m4a to flask server on Android with OkHttp?

Solution
RequestBody postBodyAudio = new MultipartBody.Builder()
            .setType(MultipartBody.FORM)
            .addFormDataPart("audio", "testRecordingFile.m4a", 
RequestBody.create(getFileBytes(),MediaType.parse("audio/*m4a")))
            .build();
private byte[] getFileBytes() throws IOException {
    ContextWrapper contextWrapper = new ContextWrapper(getApplicationContext());
    File musicDirectory = contextWrapper.getExternalFilesDir(Environment.DIRECTORY_MUSIC);
    File file = new File(musicDirectory,"testRecordingFile" + ".m4a");
    byte bytes[] = FileUtils.readFileToByteArray(file);
    return bytes;
}
implementation 'commons-io:commons-io:2.5'