After you've created a virtual Google Cloud Print™ via the StratoQ admin page you will need to share it out to your users before they can submit jobs.  You must do this through the Google interface. 

Via Groups

The best way to share out a virtual printer is via Google Groups™.  When you create a group you are able to automatically add all users in a domain, or you can bulk-add users.

When you share a printer to a group, the group owner will receive an email.  The owner can then accept the printer on behalf of all members of the group (current and future), and those users will immediately have access to the printer.

For more information on how to create this group, see the following FAQ: https://support.google.com/a/answer/66338?hl=en

Note: If the owner of the printer is also the group owner she will NOT receive an email.  You must have a separate account as the owner of the group.

Manually for each user

At the Google Cloud Print admin page you can use the "Share" button to invite users or groups to use the printer.  You can also allow anyone with the link to use the printer.  For more information, see Google's FAQ.

https://support.google.com/cloudprint/answer/2541899?hl=en

If you are sharing a printer out with individual users they will receive an email, and they will also need to accept the printer in the Cloud Print interface.  If the user does not do this, she will not see the StratoQ printer in the print dialog and also will not be able to submit print jobs via the mobile app.