Didn't need to/ needn't have p.p

[maral55]

Hi

I have been told that there is difference between the meaning of these two.

we needn't have paid/ didn't need to pay to get in to museum. It was free.

which one is correct and why?

Thanks in advance.

 

[Kondorosi]

needn't have p.p = Something was not necessary, but you still did it.
did not need to = Something was not necessary.