How do I stop staff entering wrong data?
You stop asking people to remember and let the software refuse it instead. In PaprPlain you write the rule down once, in your own words — a dispatched order must have a tracking number, a party who owes money must have a follow-up date, the same order number cannot be used twice — and from then on anything that breaks it simply will not save. The person is told which box is wrong and taken straight to it, so they fix it there and then rather than you finding it three weeks later. It also holds your work to its proper order, so a job cannot be marked finished before it was started, and a cancelled one does not quietly come back to life.
In your own words
Say what must be filled in, what cannot be entered twice, and what has to be true before something can move on. Dispatch an order and the delivery can be raised by itself. What it does.