Calling a Cloud Function from Android through Firebase

 Declare the dependency in app/build.gradle.

dependencies {   
    implementation platform('com.google.firebase:firebase-bom:30.1.0')

    implementation 'com.google.firebase:firebase-functions'

}

private FirebaseFunctions mFunctions;
// ...

//In Activity 

mFunctions = FirebaseFunctions.getInstance(); 

private Task<String> addMessage(String text) {
    // Create the arguments to the callable function.
    Map<String, Object> data = new HashMap<>();
    data.put("text", text);
    data.put("push", true);

    return mFunctions
            .getHttpsCallable("addMessage")
            .call(data)
            .continueWith(new Continuation<HttpsCallableResult, String>() {
                @Override
                public String then(@NonNull Task<HttpsCallableResult> task) throws Exception {
                    // This continuation runs on either success or failure, but if the task
                    // has failed then getResult() will throw an Exception which will be
                    // propagated down.
                    String result = (String) task.getResult().getData();
                    return result;
                }
            });
}

//Handle Error on client/user side

addMessage(inputMessage)
        .addOnCompleteListener(new OnCompleteListener<String>() {
            @Override
            public void onComplete(@NonNull Task<String> task) {
                if (!task.isSuccessful()) {
                    Exception e = task.getException();
                    if (e instanceof FirebaseFunctionsException) {
                        FirebaseFunctionsException ffe = (FirebaseFunctionsException) e;
                        FirebaseFunctionsException.Code code = ffe.getCode();
                        Object details = ffe.getDetails();
                    }
                }
            }
        }); 

private FirebaseFunctions mFunctions;
// ...
mFunctions = FirebaseFunctions.getInstance();

private FirebaseFunctions mFunctions;
// ...
mFunctions = FirebaseFunctions.getInstance();

private FirebaseFunctions mFunctions;
// ...
mFunctions = FirebaseFunctions.getInstance();