1999 Subaru Wagon Wagon Door

Got a quick on the wagon door of my 99 subaru legacy wagon.

The wagon door is simply stuck. It will lock and unlock. I can put the key in a turn it. The door won't budge. We've sat in the rear and pushed with feet while pulling from outside.

Is this a structural problem? A key problem? Do I take it to a body shop? Dealer?

Any advice would be huge.

Thank you much.