userVerification.java

private void userLogin(String email, String password) {
        showProgressDialog();

        mFirebaseAuth.signInWithEmailAndPassword(email, password)
                .addOnCompleteListener(new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        Log.d(TAG, "signInWithEmail:onComplete:" + task.isSuccessful());
                        if (!task.isSuccessful()) {
                            Log.w(TAG, "signInWithEmail", task.getException());

                            Toast.makeText(LoginActivity.this, "Произошла ошибка. Введены неверные данные или такого пользователя не существует",
                                    Toast.LENGTH_LONG).show();
                        } else {

                            checkIfUserApproved();

//                            Intent intent = new Intent(getApplicationContext(), MainActivity.class);
//                            startActivity(intent);
//                            finish();
                        }
                        hideProgressDialog();
                    }
                });
    }

    private void checkIfUserApproved() {
        final String userID = currentCourier.getUid();

        mDatabaseReference.child("couriers").child(userID).child("verified")
                .addValueEventListener(new ValueEventListener() {
                    @Override
                    public void onDataChange(DataSnapshot dataSnapshot) {
                        String userVerified = dataSnapshot.getValue(String.class);

                        // TODO: Debug
                        Toast.makeText(LoginActivity.this, "VALUE: " + userVerified,
                                Toast.LENGTH_SHORT).show();

                        if (Objects.equals(userVerified, VERIFIED_TRUE)) {

                            mPreferences.setUserMode(COURIER_VERIFICATION, VERIFIED_FALSE);

                            Intent i = new Intent(LoginActivity.this, MainActivity.class);
                            startActivity(i);
                            finish();

                        } else {
                            mPreferences.setUserMode(COURIER_VERIFICATION, VERIFIED_FALSE);
                            startActivity(new Intent(LoginActivity.this, RequestSentActivity.class));
                            finish();
                        }
                    }

                    @Override
                    public void onCancelled(DatabaseError databaseError) {

                    }
                });
    }