I can not delete a cash sale . Encountered this error .. Can anyone help regarding this

Open that cash sale, and click on “Related Records” sub tab. It will show you any related records to this Cash Sale. Those entries need to be deleted individually first before deleting the cash sale. Also accountants recommend not deleting, but rather creating a return/ adjustment/ etc instead. This way you can reverse the transaction and all its financial effects - and capture the reasons why in the comments section.