So this sort of production line require massive amount of setup and tooling etc. So Orders Clauses are used all the time.
All Rough Estimates and figures here on out.
Ok So say they were Contracted to buy $12B of screens say 200 Million screens
Samsung will have geared up to produce that many over time. Supply chain in place, people, Factories, Transport etc. To be made and delivered week by week.
Apple Targets are low ( Say 150 million ) they only need so lower the order triggering the under order clause where they probably pay about 25% on the under delivery which would be about $950 Million of the $4 Billion
Note - the displays will not have been made yet. Apple are all about Just in time production. So no warehousing of parts. 100K Screens are delivered at beginning of week 1 to Foxconn and 100K iPhones Plop out full made and boxed at the end of week one.
The Negative - Obvs Losing $950 Million.
The Positive - Save $3 Billion Dollars.
The Alternative Pay the Full amount - Warehouse 50 Million screens with Associated Transport / Storage / Security.