I’m a builder, and this is an absolute shit job. There’s a lot more issues than the just the railing. I wouldn’t pay this guy at all and I’m usually biased towards the contractor. There’s a few ways that this can be fixed but they are all a lot of work to do. If you want to discuss all the things I see wrong and options on how to make it somewhat looking correct you can pm me and we can talk over the phone or something.
I think the best way to fix it would be to start at right railing and have the railing installed between the posts like the left railing. But that would also require for the height of it to be shortened so that the bottom of it is over the stairs, not next to it like left side.
Next remove the front landing rail and rebuild it longer it so the post is over the stairway. Then remove left railing, mount lower post on the step like the right railing, and finally reinstall the stair railing post to post. Of course after it’s shortened to match the new right railing.
Make sense?