Sellers receive emails notifying them of subscription sales. Because it's possible to make a one-time "subscription", we send emails for one-time payments with confusing terms.
"One-time payment" could be less confusing, and the reference to a next payment just needs to be removed. These emails for donations also reference one-time donations, and next payment to be received.

Started working on this in D47311-code
@sixhours can we close this one out now that D47311-code has landed? or do we need additional patches?
Yep! All done.