Question
Provider needs to add Order Detail to the order in status "Waiting for payment". Order details will be of "Non Provisioning item" type.
However this operation brings error:
Detail Line cannot be added to Order in Status 'Waiting for Payment after provisioning'.
or
Detail Line cannot be added to Order in Status 'Waiting for Payment'.
Answer
Order Flow customization is required to allow this operation for Sales Orders in "WP" status. Provider need to open order flow (changes only possible for non-default order flows), open "SO" order type, open Order Status "WP", press Edit and mark "Is Addable" check box.
Changes are applied immediately. No restart of the system or Order resubmission is necessary.