You can hold someone to a deadline and still be kind. “What do you need to hit Friday?” does both.

Firmness and warmth get treated as a dial you slide between, so people pick one and drift. A question that assumes the deadline holds and offers help with it does both at once: the date is not negotiable, and you are on their side about getting there. It also reveals the actual obstacle, which nagging never does.

Replace the reminder you were about to send with a question about what would make the date possible. Then supply whatever they name, if you can. If the deadline genuinely cannot hold, you will find that out now instead of Friday.