Let's get this sorted out so you can lodge the client's Single Touch Payroll (STP).
You may have registered the supplier ABN, and that's why the setup failed. It is the business ABN that must be registered. The tax agent is NOT permitted to contact the ATO on behalf of the business. Therefore, an authorised contact of the business must contact the ATO to register.
I've got the steps to enable electronic lodgement so you can use STP:
Electronic Lodgement & STP
Go to Employees from the left navigation bar.
Select the Payroll Settings tab, then click ATO Settings.
Go to the Electronic Lodgement & STP tab.
Contact the ATO on 1300 852 232 and provide them your Software Provider and Software ID or update your details through Access Manager.