One of the hassles with onboarding new users with DEAR is explaining and getting clients and their team members to understand Simple vs Advanced vs Service Purchase and Sale tasks and when to choose which.
In my opinion - it would be much simpler and better for the user experience of the software long term if you guys were able to redesign the UI so that there is only one type of Purchase and Sale that you can create, and the functionality within those tasks allows for all scenarios.
I would have it setup as you have your Advanced layout currently setup. Then, if it's a simple purchase, you just enter one Invoicing & Receiving and its done. Or, you can enter more. Or, you can just have Service items in the order and the system doesn't throw any errors.
If I am way off base and these separate types are required, I would love to hear some feedback. Otherwise I just think this could be consolidated and make it so much easier to use for those employees of our clients who find it difficult.