What is a require condition in NPL, and what happens when one fails?

A require is a runtime boolean assertion inside the business logic; if it evaluates to false, the Runtime generates a custom error and returns it as a REST response.

require conditions are safeguards against invalid or unexpected user actions — including ones nobody anticipated at design time. Each one asserts that some boolean expression must hold at Runtime (for example, "the amount must be positive" or "this can only happen while verified"). When a require fails, the Runtime does not silently continue: it produces a custom error message and returns it as a REST response, so the calling backend integration service or frontend can handle it appropriately and show the user something meaningful. This turns invalid input into a clear, catchable error rather than a corrupt state change.