The Document Builder may ask you to provide your Company Number to make sure your company is properly identified in the legal agreement you're creating.
Its easy to get the numbers mixed up. The number you're looking for here is on your Certificate of Incorporation, and it's likely to be on any company resolutions that have been passed (for example bank opening documents).
This handy guide explains the difference between the Business Registration Number (BR) and your Company Registration (CR) number.
Company paperwork (often called Company Secretarial) can be fiddly. Having a lawyer advise you on this can make the process quicker and easier. Find out more about how you can work with a lawyer right from the Zegal App, and get legal advice whenever your business needs it.