Firebase Realtime Database Functions pagination Android

Question

Currently my app gets all the data from the realtime database and filters through it and sends it back to android where the data is shown in a recycler view. How do I paginate my data so the user does not have to wait for the whole thing?

Firestore Function:

exports.getRecipes = functions.region('europe-west1').https.onCall((data, context) => {

    const categories = data.categories;
    const ingredients = data.ingredients;

    recipesToReturn = [];

    const eventsData = Promise.all(categories.map((category) => {
        return admin.database().ref(category).once('value').then((snapshot) => {

            snapshot.forEach(function (childSnapshot) {
                if (canBeMade(childSnapshot.val(), ingredients)) {
                    recipesToReturn.push(childSnapshot.val());
                }
            });
            return recipesToReturn;

        });
    }));

    return eventsData;

});

Android Studio:

getRecipes().addOnCompleteListener(new OnCompleteListener<ArrayList<Recipe>>() {
            @Override
            public void onComplete(@NonNull Task<ArrayList<Recipe>> task) {

                if (r.size() <= 0) {
                    progressBar.setVisibility(View.GONE);
                    Toast.makeText(RecipesActivity.this, "Nema recepata", Toast.LENGTH_SHORT).show();
                    return;
                }
                for (int i = 0; i < r.size(); i++) {
                    recipes.add(r.get(i));
                    adapter.notifyItemInserted(i);
                }
                progressBar.setVisibility(View.GONE);

            }
        });

private Task<ArrayList<Recipe>> getRecipes() {
        Map<String, Object> data = new HashMap<>();
        data.put("categories", categories);
        data.put("ingredients", ingredients);

        return mFunctions
                .getHttpsCallable("getRecipes")
                .call(data)
                .continueWith(new Continuation<HttpsCallableResult, ArrayList<Recipe>>() {
                    @Override
                    public ArrayList<Recipe> then(@NonNull Task<HttpsCallableResult> task) throws Exception {
                        ArrayList<ArrayList<HashMap<String, Object>>> result = (ArrayList<ArrayList<HashMap<String, Object>>>) task.getResult().getData();
                        ArrayList<Recipe> recipes = new ArrayList<>();
                        for (int i = 0; i < result.size(); i++) {
                            for (int j = 0; j < result.get(i).size(); j++) {
                                recipes.add(new Recipe(result.get(i).get(j)));
                            }
                        }
                        return recipes;
                    }
                });
    }