FechData.java

  //function to fetch payment data from the database
    private void fetchPaymentUsers()
    {

        payRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for (DataSnapshot snapshot : dataSnapshot.getChildren()) {

//creating an object and setting to displlay
                    Constants pays = new Constants();
                    pays.setFirst_Name(snapshot.child("FirstName").getValue().toString());
                    pays.setOther_Name(snapshot.child("OtherName").getValue().toString());
                    pays.setPhone(snapshot.child("Phone").getValue().toString());

                    //this just log details fetched from db(you can use Timber for logging
                    Log.d("Payment", "Name: " + pays.getFirst_Name());
                    Log.d("Payment", "othername: " + pays.getOther_Name());
                    Log.d("Payment", "phone: " + pays.getPhone());

                    /* The error before was cause by giving incorrect data type
                    You were adding an object of type PaymentUsers yet the arraylist expects obejct of type DisabledUsers
                     */
                    paymentUsersList.add(pays);


                }
                //create a pdf file and catch exception beacause file may not be created
                try {
                    createPaymentReport(paymentUsersList);
                } catch (DocumentException | FileNotFoundException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

    }