I want to be able to send push notifications using Titanium on Android. However I get a back-end error whenever I try this, which I believe is to do with invalid credentials. I
When I did this I created an API Key, not an OAuth client ID. Same screens you had, but choose API Key from the Create credentials dropdown.
Here's a snip from my notes:
Create a Google API Project
The first step is creating a Google API project and enabling its GCM service. You also need to obtain a GCM sender ID and create a Google API server key.
create/edit a project from here : https://console.developers.google.com/project
After it is created, click the hamburger menu in the upper left, and Mouse over API Manager and choose Credentials
On the Credentials tab Click Create Credentials and choose API Key
copy it and paste it into the Arrow dashboard
Click hamburger menu - IAM & Admin -> Settings copy the project number - paste that into Arrow dashboard