The first room every legitimate guest passes through. Registration is where the prescription is confirmed — the document a licensed prescriber writes so that a licensed pharmacy may dispense. Nothing crosses a licensed U.S. counter without it, and no online seller is a shortcut around the rule.
A hotel that lets a guest into a room without checking them in is not a hotel. It is a warehouse with bedding.
Confirm the prescription exists before opening any seller's site. If it does not exist yet, no amount of elegant web design changes the next step — which is your prescriber, not the internet.