The SI is the source document the draft BL is built from, so an error or a late submission against the carrier's SI cut-off turns into amendment fees or a missed sailing. Each carrier has its own SI portal, its own accepted format, and its own cut-off timing, which is much of what makes carrier-specific SI handling worth automating.
Glossary
Shipping Instruction (SI)
The shipper's formal instruction to the carrier on how to draw up the bill of lading: shipper, consignee, notify party, cargo description, marks, and the rest of the BL detail. It is submitted after the booking and before the BL cut-off.