Select Costing Options - Transactions tab, and select Compulsory Costing, this imposes costing for all transactions, unlike the two alternatives below, which are more precise in their operation.

Select Accounts, You can set a flag against a Nominal Account, so that any Transaction Detail line which will be posted to that Nominal Account (determined by the Analysis Code), will be forced to have Costing details entered.

Select Analysis, You can set a flag against particular Analysis Codes, so that any Transaction Detail line which uses them, will be forced to have Costing details entered.