Product type, size range, quantity, market, target cost and any must-have feature. A reference photo is more useful than a paragraph of description.
The piece is drawn as a flat layout with fold lines, slots and glue tabs. This is where the shape is proven on paper: if it cannot be drawn cleanly, it cannot be cut cleanly.
An unprinted sample shows whether the structure stands, folds and fits. Approve this before any artwork is applied.
Print files are laid onto the approved dieline. Sending artwork before the dieline is fixed is the single most common cause of delay, because every structural change re-opens the print.
The printed sample is what you sign off. Check the cut edges, the glue line, the colour against your reference and the fit of any inserts.
Bulk runs from the approved sample. Changes after this point mean a new sample, and a new date.
None of these are technical problems. They are sequencing problems, and they are the cheapest thing to fix.