[masaegu]

「別にいいのに」 can mean so many different things depending on where one says it. It would help if you gave the context in which you saw or heard this phrase. Meanwhile, if one of the following phrases seemed to fit, then that would probably it for you.

1. You didn't have to do that.
2. It doesn't really matter to me.
3. I didn't quite expect (something).

We say 別にいいのに very often. It's this kind of everyday phrase that makes your Japanese sound like Japanese.

これからも頑張ってください！