Never offer cash tips on delivery platforms. People occasionally claim in their delivery instructions that they will pay an additional cash tip; nobody actually does. Talk to any driver and they will tell you the same: cash tippers are non-tippers.
Drivers can’t even see your offer of a cash tip until after they have accepted the offer. If you don’t offer a tip at checkout, your cash-tip offer is completely indistinguishable from a no-tip offer.