This site states this directly under its manufacturing claims: each package is described as a one-time purchase, with no automatic subscription or recurring charge.
Recurring, hard-to-cancel subscriptions are a common complaint in the supplement category generally — worth crediting this site's direct no-auto-billing claim, while still confirming it yourself at checkout before you pay.
This site's own FAQ is direct: confirm the current purchase structure directly at checkout before ordering, including whether it is a one-time purchase or involves recurring billing, since terms can change.