Which document do you actually need?

Nearly the same fields, opposite jobs. One quotes a sale that has not happened; the other records one that has.

Same statement about where goods were made. The difference is who vouches for it, and whether your destination accepts your word.

Both price a sale that has not happened. One is an indication, the other is close to an offer your buyer can accept.

One values goods for customs. The other evidences tax for a buyer reclaiming it. Exports often need both, saying different things.

Something on the invoice is wrong. Whether you issue a credit note or reissue the invoice depends on whether the document was wrong or the deal changed.

Same document, two levels of detail. HS codes and per-item dimensions matter on some shipments and are noise on others.

One instructs your forwarder and authorises them to act for you. The other tells the carrier how the bill of lading should read.

A purchase order is the buyer's offer on the buyer's terms. A sales contract is both parties agreeing one set. Which one is in force decides whose terms apply.