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.

An end date you set yourself stays, even when you delete the version after it. The days after that end then have no rule, and the Overview flags them under Needs your attention, for example No fee rule or No shipping price.

To delete a version, open the cost's history and click the three-dot menu on it. The menu reads Delete this version on Logistics, in Price history, and on Transaction fees, in History. On Products it reads Delete this cost, in Cost history. A dialog says first what then counts for those days, and Delete confirms.

On the Overhead page the button in a cost's panel reads Delete cost, or Delete spend for marketing spend: click it, then click again to confirm. A CSV import has Delete import, which removes all its rows. An overhead cost or marketing spend you changed from a date is two costs, the earlier one ending the day before. Delete the later one and the earlier one runs on again, unless you moved its end since. Any other overhead cost simply comes off its days.

A variant's unit cost can be deleted too. If a cost came before it, that cost runs on in its place. If it was the variant's only cost and Shopify holds a Cost per item, Shopify's cost comes back with the next sync, for every order since your first. Without one, the orders count no product cost and are flagged until you add one.

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, correcting it is the better fix. And if the cost simply stopped, set an end date on the rule instead.