Earlier quoted context omitted.
That would however mean the delivery person will believe you intend to tip zero until you actually do. Not discussing whether it is right or not, but I assume that could affect the received service.
Given that the vast majority of situations in which you tip (notably waiters, waitresses and other staff) result in the tip being given after service, and not before, I'm OK with that.
The delivery person will be able to see your intentions of tipping zero, as nothing else is communicated.