Haha im on the same road, its hard indeed and as you say most of the tutorials out there are for spark and not particle.
Have a look at this guys tutorial, he accomplish what you want but in a slight different way.
But atleast its a great tutorial but he dont use the particle-api-js as of now.
So i guess if you are doing this because you want to learn the particle-api-js
or that you just want to make it work on your local wifi.
Also we have rickkas7 tutorial, ofcourse 
Someday when i have the time i want to collect all this tutorials in one thread for easy access and a explanation what they do.
So for the issue you are getting, check your version, They corrected some user-agent issues in version 5.2.3, (It could be after this your issue started aswell?, what version did you have when it was working?, look at the official git location and check closed issues.) so if you are using an older version you might encounter issues.
else i guess you should make a new thread about the issues.
Remember to add alot of information of the issue, i tend to always forget that.
Hope you can continue the project, i will bang my head to the wall untill i have a working app atleast 
BR
Dimi