While one-time payments are a great feature idea, we must stay true to what Patreon is all about: Building a membership platform for creators.
At the moment, Patreon only offers recurring memberships, and one-time donations are not available. All Patreon memberships recur on a monthly or annual (if your creator has this available) billing cadence. You can learn more about how creators can bill their patrons in our article: Understand my payments to creators.
The best way to make a one-time payment is to sign up and then cancel the membership after you've been charged. You'll know when your payment has gone through because you'll receive an email confirmation.
Additionally, you can check your billing history to review payment details.