I'm trying to use the GA measurement protocol to track usage of my app, however there doesn't seem to be a hit you can send in order to specify the OS.
I'm therefore assuming (though it's not clear) that the OS is extracted from the User-Agent header, however regardless of what user agent I report, the OS always seems to come up as 'not-set'.
Has anyone got any tips on how to specify the OS?
AFAIK, you still cannot specify the OS, through the MP, as that is specified through the user-agent, as you've mentioned. Similar question asked here: https://groups.google.com/forum/#!msg/google-analytics-measurement-protocol/5S4xEAxd1_o/ed9PJrOzd_UJ
A similar question asked in SO: https://stackoverflow.com/questions/22694992/unviersal-analytics-measurement-protocol
Using the User Agent string works fine, just make sure that you are sending the string and that the data that you send will satisfy any filters that you have set up on your GA Property.
