Add-ons are for materials or costs that fall outside the stated scope of a service but don't require a separate service line. Think: extra plumber's tape when replacing a wax ring, or new toilet bolts when reinstalling a toilet.
If you need something that's not listed in the parts section, that can be added to the add-ons section.
Use them sparingly. Lula has done significant work to price labor and common materials into the base service cost. Add-ons exist for the unexpected — not as a way to add charges on top of an already-scoped service. Each add-on has a cap, so you won't be able to submit amounts over that limit.
Do not use add-ons to add labor for work that should have its own service line, or to charge for materials that are already included in the scope.