Unable to create call adapter for io.reactivex.rxjava3.core.Observable<java.lang.Object>

Question

I'm using Retrofit as a network client and sending Multiple APIs using RxJava's zip API, but when I create an instance for Retrofit, I got this error,

java.lang.IllegalArgumentException: Unable to create call adapter for io.reactivex.rxjava3.core.Observable<java.lang.Object>
                     for method ListingApiService.sendMessageOffer1
                    at retrofit2.Utils.methodError(Utils.java:54)
                    at retrofit2.HttpServiceMethod.createCallAdapter(HttpServiceMethod.java:116)
                    at retrofit2.HttpServiceMethod.parseAnnotations(HttpServiceMethod.java:67)
                    at retrofit2.ServiceMethod.parseAnnotations(ServiceMethod.java:39)
                    at retrofit2.Retrofit.loadServiceMethod(Retrofit.java:202)
                    at retrofit2.Retrofit$1.invoke(Retrofit.java:160)
                    at java.lang.reflect.Proxy.invoke(Proxy.java:1006)
                    at $Proxy2.sendMessageOffer1(Unknown Source)
                    at com.thunderboar.nutshellwhatsapp.BottomSheet.BottomSheetFragment$3.onClick(BottomSheetFragment.java:280)
                    at android.view.View.performClick(View.java:7441)
                    at com.google.android.material.button.MaterialButton.performClick(MaterialButton.java:1194)
                    at android.view.View.performClickInternal(View.java:7418)
                    at android.view.View.access$3700(View.java:835)
                    at android.view.View$PerformClick.run(View.java:28676)
                    at android.os.Handler.handleCallback(Handler.java:938)
                    at android.os.Handler.dispatchMessage(Handler.java:99)
                    at android.os.Looper.loopOnce(Looper.java:201)
                    at android.os.Looper.loop(Looper.java:288)
                    at android.app.ActivityThread.main(ActivityThread.java:7839)
                    at java.lang.reflect.Method.invoke(Native Method)
                    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:548)
                    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1003)
                 Caused by: java.lang.IllegalArgumentException: Could not locate call adapter for io.reactivex.rxjava3.core.Observable<java.lang.Object>.
                   Tried:
                    * retrofit2.adapter.rxjava2.RxJava2CallAdapterFactory
                    * retrofit2.CompletableFutureCallAdapterFactory
                    * retrofit2.DefaultCallAdapterFactory
                    at retrofit2.Retrofit.nextCallAdapter(Retrofit.java:272)
                    at retrofit2.Retrofit.callAdapter(Retrofit.java:237)
                    at retrofit2.HttpServiceMethod.createCallAdapter(HttpServiceMethod.java:114)
                    ... 20 more

this is the implementation

public interface ListingApiService {

      @POST("{id}/msg")
        Observable<Object> sendMessageOffer1(@Path("id") String pid,
                                             @Body MyModel myModel
        );

    }

Retrofit instance

  String BASE_URL="https://mywebsite.com";
  String VERSION="v11.0/";
    
   Retrofit retrofit = new Retrofit.Builder()
                      .baseUrl(BASE_URL+VERSION)
                      .addConverterFactory(GsonConverterFactory.create())
                      .addCallAdapterFactory(RxJava2CallAdapterFactory.create())
                      .client(new OkHttpClient().newBuilder().addInterceptor(new 
                        MyIntercepter()).build())
                       .build();

Intercepter class

public class MyIntercepter implements Interceptor {

    private static final String TAG = "MyIntercepter";
    @Override
    public Response intercept(Chain chain) throws IOException {
        Request request=chain.request();
        Request newRequest=request.newBuilder()
                .header("Authorization","Bearer token")
                .header("Content-Type","application/json")
                .build();

        return chain.proceed(newRequest);
    }
}

the dependencies

implementation "io.reactivex.rxjava3:rxjava:3.0.0"
implementation 'io.reactivex.rxjava3:rxandroid:3.0.0'
implementation 'com.squareup.retrofit2:adapter-rxjava2:2.9.0'
implementation 'com.squareup.retrofit2:converter-gson:2.9.0'
implementation 'com.squareup.retrofit2:retrofit:2.9.0'
implementation("com.squareup.okhttp3:okhttp")

What went wrong with this implementation,

Answer 1

The issue because of the com.squareup.retrofit2:adapter-rxjava, we have to update to version 3, like below

previous

com.squareup.retrofit2:adapter-rxjava2:2.9.0

need to update to

com.squareup.retrofit2:adapter-rxjava3:2.9.0