Start with the part that is verifiable
Separate the event you can describe from the motive or reaction you are guessing. For a message about how to apologize for not attending an event, use this factual base: confirm the booking, timing, guest, transport, or budget change and who now has to adjust.
Make one answerable request
Give the recipient one concrete question or next step instead of several emotional jobs at once. Offer a replacement plan, reimbursement, or clear decision before the next real deadline. Make the immediate next step clear enough that the recipient can answer without reconstructing the entire history.
Leave the recipient in control
Do not minimize lost money or time, and do not invite extra people into a plan without consent. Follow venue, transport, insurance, and local safety rules when an emergency or stranded traveler is involved. A clear message remains useful even when the answer is no or no answer arrives.