Paying down the technical debt is a tricky one, especially if your application is large. If you have the cash, it might be worth it to bite the bullet and hire

Paying down the technical debt is a tricky one, especially if your application is large. If you have the cash, it might be worth it to bite the bullet and hire a consultant/freelance technical writer. Get them to build up the documentation that you are missing, and then make sure your workflow enforces that it stays up to date.