Build it in slices.
Incremental adds finished pieces. Iterative refines a rough whole. The best delivery does both, a point Jeff Patton made famous with his Mona Lisa sketches.
Incremental
Piece By Piece
Finish the login, then billing, then faults.
Risk: nothing useful end to end until the last piece lands.
Iterative
Rough, Then Better
Sketch the whole thing, then refine it.
Risk: it never quite gets finished.
Both
Thin And Whole
One useful slice, end to end, then improve.
Customers get value early, and you learn fast.
Source: Jeff Patton & Associates: Don't Know What I Want, But I Know How to Get It ↗
Thin, whole, useful. Then better.