In many cases, you can take steps to bring your business into compliance after operating without registration. The process depends on your business activities, how long you have been operating, and the laws in your jurisdiction.
Formalizing your business may involve registering the business, obtaining required licenses or permits that were previously missing, addressing tax obligations, reviewing prior tax filings, paying any interest or penalties, evaluating contracts entered before registration, and updating banking, insurance, and vendor relationships where appropriate, as well as your business records. Registering now does not automatically resolve issues from prior years, but it can help establish a stronger foundation going forward.