In reply to gimmergimmer:
I always recommend clients take out insurance to cover them in case of not being able to attend, but never suggest any specific policies. Actually advising on insurance requires proper licensing and registration.
BMC will cover you for illness or injury stopping you attending, have a look at page 6 here: https://www.thebmc.co.uk/modules/insurance/r/downloads/BMC%202021_22_1221%2...
Other than that, what could you imagine going wrong? Probably worth checking any general travel insurance policies will cover you for rock climbing/mountaineering, if that's not an activity covered on the insurance it's unlikely that the booking would be covered.