How do I add or delete a Custom category?

Open a cost on the Overhead page and click its Category. At the end of the list, click Custom category. Type a name, like Insurance, and click Add.

Your category is saved with the cost. From then on it is offered under Your categories. It still counts as overhead, line 31 of your P&L. It only groups your costs under your own name, here and on Insights. If you type the name of a preset, like Salaries, the preset is picked, so you never get two of them.

To delete one, point at it in the list and click the bin. A category that no saved cost uses goes at once. A category in use asks first, then moves its costs to Miscellaneous. No number on your P&L moves either way, because they all stay overhead.

If your category sounds like advertising, like an agency running your ads, the form points you to Marketing spend instead. Ad costs belong there, because they count before CM3. CM3 is what you keep after marketing too.