I have event organisers that have cancellation policies that depend on the number of days prior to the event that an event is cancelled.
They only take payment offline after the event has taken place in accordance with their cancellation policy.
It would be really useful to record in the registrants table the date and time of a cancellation so that they can apply their cancellation policy when manually calculating final payment.
[And even better if events could be configured for % or amount of fee to be paid at different cancellation dates/times and have these applied at time of cancellation in order to calculate the final payment due (for after event offline payments) or refunds due if payment has already been taken. But for now I'd be happy with just recording the date cancellation is made.
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