From OCS Support Wiki

Introduction

You may need to locate the service ID of a particular service in your account. This guide will show you how to do this.

Billing System Login

You will need to login to our billing system with your client ID and password. You can find this in your welcome letter.

Service ID

Once you login, click the "x Active Service(s)" link in the top right hand corner. This will bring you to a page with your current active services with us. Your service ID is the number under the "ID" column next to the service in question.