There are a few posts with answers to similar issues.
Maybe you can adapt one of the solutions:
- What's the right way to "expose" v6 beta via swag (nginx reverse proxy)? - #5 by MadaxDeLuXe
- Can't get v6 webinterface behind nginx reverse proxy to work - #4 by stefan
Note:
I just added 2 links here, but you can use the search to find more similar issues.