Fill a last-minute cancellation fast

Help me fill a last-minute cancellation, quickly.

My business: [e.g. hairdresser, physio, dog groomer, tutor]
The slot: [day, time, how long]
What it could be used for: [service]
Who I can message: [e.g. waiting list, regulars, Instagram followers]
Anything I'll offer: [e.g. nothing, a small extra, a discount]

No questions needed unless something's unclear: I'm in a hurry.

Then give me:
1. A short text or WhatsApp message, under 30 words.
2. A social post or story, under 30 words.
3. A message to my waiting list, first come first served.
4. An idea to cut cancellations in future, such as a reminder message or a waiting list.

Quick, friendly, no fake urgency, UK English.

Stay in this ChatGPT chat. Do not turn on apps or connectors, and do not use memory from another chat.