Implement Google Play Services after implementing Google ADMOB

Hello Everyone

I have successfully implement Google ADMOB using this tutorial (https://www.youtube.com/watch?v=q5T98X3EawA).

It works perfectly and i have no problems... Until i decided to try add Google Play Services(GPS) (https://github.com/playgameservices/play-games-plugin-for-unity)

I have watched many tutorials on how to get this working (none from 2016), but i have not managed to get it working. I have set up my dev console up ready for GPS, but when i tried to implement it, my game would crash, and ADMOB would not work (ad banners/ interstitial would not load). I am looking for a step-to-step process of how to get GPS working along with ADMOB. The process i did for configuring GPS was:

1. Sign my app with a keystore and put in my package name etc.

2. Build my app and upload to dev console

3. Link my app with the service and get my OAuth client ID

4. Create achievements/ Leader boards

5. Import Google Play Services Plugin package

6. Setup the service in the android setup dialog (i.e. the screen where you get prompted for the "get resource" resources) - says configured successfully

7. Build the apk successfully

8. Test on phone where neither ADMOB or GPS work.

I do not get any compiler errors during any of the above.

My SDK manager resources are all up-to-date. i have GPS installed and all other required resources in SDK manager.

I'm using Unity 5.3.4

I am available to skype if someone could guide me through this process using a dummy/ new project.