[Question] "be going to do" "be supposed to do"?

Frequently I hear people using "be suppose to do smt". I understand what they mean and sometimes I also use it.

But I'm not sure about the difference between "be going to do" and "be suppose to do" .

For instance, when I say "I am going to call him" and "I am supposed to call him", is that same meaning? Or does the nuance differ from each other?

"Supposed to do" means that you really should do something, but you might not. Example: I'm supposed to clean up my room, but I won't do it. When you are supposed to do something, it might  be because your parents or your boss told you to, or that it's something you need to do oftne. A common phrase is "to do what you're supposed to" which means you are *going* to do what you are *supposed* to do.

When you are "going to do" something, you are saying that you will do it, either now or later.