tos clarification for "promise of recompense"

[rms-joe]

The user agrees not to use the service for financial transactions that are not donations, notably those linked to the execution of a contract or a promise of recompense.

from the phrasing it is unclear to me if little perks for people donating to a project are allowed.

example: on request we sent you a stickerpack if you donated >10€

it is a real donation, but on the other hand a promise to sent something as well.

if something like that would be valid, is it possible to rephrase the sentence in a way that it is unambiguous?