Had the time to play more with it and I think you do not do `record_route()` for OPTIONS requests -- this is a requirement to know local addresses used to communicate with each side, the Record-Route headers do not appear in the requests sent out. I pushed a commit to the docs to make this clear.
I also added another patch (97532ca18f595d89edf9b0b6e6688847aa38dd44) that should make it work without `record_route` for your specific case, but I would recommend to do the option with `record_route()`, should be safer overall.
Reopen if still an issue.