To create a membership that only has one payment and lasts for a certain time period follow the steps below.
In the Finance section, under Products select Add New Membership.
Populate the fields as required, making sure to enter the Number of payments collected as 1, if you are only looking to bill the member once and click Save.
You can then apply this Product to relevant Members under the Subscription section. When applying as a Subscription enter the End Date which is relevant for the time period the Subscription covers e.g. End Date the subscription 12 months from today.