MoCRA asks a brand to register its facility and list its products with FDA. REACH24H does that, renews it each year, acts as US Agent and reviews the formula, label and safety file behind it. Its own Korean page makes the point that finishing registration and listing is not the whole of US compliance.
The rest arrives by container. Each shipment needs the right registration and listing numbers for the supplier and the product lines on it, a certificate of analysis and an INCI list, an invoice that agrees with the packing list and bill of lading, and a duty figure that includes Section 301. Korean cosmetics on free-rate lines such as 3304.99.50 now pay 12.5% under heading 9903.05.71, and U.S. note 52 does not exempt heading 3304.
That is the work Senda runs, for the importer, on every shipment. It files nothing with FDA or CBP and gives no legal advice. So the two fit together: REACH24H gets the brand registered, Senda checks each shipment against what was registered, and your broker files the entry from a packet that is already complete.