Hello,
First, I would like to thank you for releasing Mattermost 2.1 and API that let us install and test your android app 
I have following questions regarding this app, 'cause I don’t know if our team is doing something wrong or there is some mix-up in documentation.
We are using Mattermost server 2.1, latest release of android app, and your push proxy code from github. We compiled .apk and installed it on our phones. Then we tried to test push notifications, with no luck, there were infos in log about sender id mismatch. We registered at https://developers.google.com/mobile/add and obtained Sender ID and Google API key. We provided API key to our push-proxy instance and change Sender ID in android app code - and everything started to work properly.
So my questions are:
- Did we do installation correctly, are we correct that teams of users, that compile their own .apk’s should also register on above Developers Page and put their own Sender ID’s in android app code?
- Is original Sender ID - 400589284558 working only with http://push-test.mattermost.com server?
Maybe, to make app avaliable in Google Play more universal - should we give users possibility to change Sender ID from app activity?
We can provide proper code to do that, as it will be great to let our users to install universal app from Google Play instead of doing that through our own compiled .apk.
Best regards!