Unable to create call adapter for io.reactivex.Observable
You need to tell Retrofit that you want to use RxJava 2, using: addCallAdapterFactory(RxJava2CallAdapterFactory.create()) So, for creating your Retrofit object, you will have something like: Retrofit retrofit = new Retrofit.Builder() .baseUrl(SERVICE_ENDPOINT) .addCallAdapterFactory(RxJava2CallAdapterFactory.create()) .build();