What is unregistered parking lot in my property tax?

Hi Friends,

I am having trouble to define ownership of parking lot which I bought with my home.

It is not there in my land transfer documents but in my property tax documents it is mentioned as “unregistered”.
Exactly what does it indicate?

My lawyer says it is exclusive use parking so it will not be there in land transfer documents but my property management says it is not in your land transfer paper so they will not deduct any maintenance for it.

Also what should be the document to prove my ownership of that parking?

Your help and opinion is highly appreciated

Thanks