Personally, I've always tried to tip with cash, putting the money directly into the server's or deliverer's hands and telling them it's for them.

I rarely trust restaurants, unless I'm a regular and know their practices very well, to hand over electronically delivered tip money to their workers. Once somebody has money, they can be very reluctant to let go of it, and things just get worse when the transaction is depersonalized and/or automated.

Do your servers and delivery people a favor. Press cash directly into their hands and tell them it's theirs and nobody else's.