I am having the same problem.

Hi any update on how to resolve this issue, we are encountering the same problem. Please see attached file for our iosbuildlog

Hi, this is an old plugin, and has been replaced by an official & supported one by Outsystems:

https://www.outsystems.com/forge/component/2119/onesignal-plugin/

Sadly it's for .NET stack only.

I got a modified One Signal Notification plugin that works for both .NET and JAVA stack, pm me if you're interested.

Hi still got the same error unableto generate the iOS mobile app. 

Looking at your Error Log, it was not OneSignal plugin error...

Error was at cordova-plugin-googleplus

Failed to install 'cordova-plugin-googleplus':Error: Variable(s) missing: REVERSED_CLIENT_ID
    at /usr/local/lib/node_modules/cordova/node_modules/cordova-lib/src/plugman/install.js:362:23
    at _fulfilled (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:787:54)
    at self.promiseDispatch.done (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:816:30)
    at Promise.promise.promiseDispatch (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:749:13)
    at /usr/local/lib/node_modules/cordova/node_modules/q/q.js:557:44
    at flush (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:108:17)
    at nextTickCallbackWith0Args (node.js:420:9)
    at process._tickCallback (node.js:349:13)
Error: Variable(s) missing: REVERSED_CLIENT_ID
    at /usr/local/lib/node_modules/cordova/node_modules/cordova-lib/src/plugman/install.js:362:23
    at _fulfilled (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:787:54)
    at self.promiseDispatch.done (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:816:30)
    at Promise.promise.promiseDispatch (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:749:13)
    at /usr/local/lib/node_modules/cordova/node_modules/q/q.js:557:44
    at flush (/usr/local/lib/node_modules/cordova/node_modules/q/q.js:108:17)
    at nextTickCallbackWith0Args (node.js:420:9)
    at process._tickCallback (node.js:349:13)