What happens when I delete a cost rule?

The rule goes, and the rule before it takes back its days. Without that, those days would have no rule at all, and the cost would quietly drop to zero.

An example: a fee of 2,9% ran until 31 May, and a new fee of 2,5% started on 1 June. Delete the June rule, and the 2,9% rule runs again from 1 June. Every day from 1 June is then worked out again. Nothing before 1 June moves.

To delete, open the rule on the Logistics or Transaction fees page. Click Delete rule, then click again to confirm. On the Overhead page the button reads Delete cost, or Delete spend for marketing spend. A CSV import has Delete import, which removes all its rows. An overhead cost has no chain of versions, so deleting it simply takes it off its days. A product's unit cost cannot be deleted. Save a new one instead.

Deleting the very first rule of a chain repairs nothing, on purpose. A chain is all the versions of one rule, one after another. Stretching the next rule back over old days would price them with a value that was never true then. That is what the effective-dating rule forbids. Those days go back to having no rule, and any flag about it comes back.

If the old value was only mistyped, editing the rule is the better fix. And if the cost simply stopped, set an end date on the rule instead.