Can something be truely moral if you get a reward for doing it?

If I get paid a lot of money to help others, is it still morally correct? If I’m good just to get into heaven is it still morally correct?

Isn’t morality just being good for the sake of good? If this is true then can any theist be truly moral or is it only non-believers that can be truly moral?

I believe that I’m good, kind and sweet to people but when I die I rot in a box. You might believe that when you are good, kind and sweet to people, you’re laying a foundation for your eternity.