Restore deleted (?) Google OAuth client app for production system

For everyone who has this problem too. Found the solution:

Project owners can restore a deleted project within the 30-day recovery period that starts when the project is shut down. Restoring a project returns it to the state it was in before it was shut down. Cloud Storage resources are deleted before the 30-day period ends, and may not be fully recoverable.

Some services might need to be restarted manually. For more information, see Restarting Google Cloud Platform Services.

To restore a project:

Go to the Manage Resources page in the Google Cloud Platform Console.

In the Organization drop-down in the upper left, select your organization.

Below the list of projects, click Resources pending deletion.

Check the box for the project you want to restore, then click Restore. In the dialog that appears, confirm that you want to restore the project.

Source: https://support.google.com/cloud/answer/6251787?hl=en