I accidentally overcharged on postage - it was £3.65 rather than the £6.50 I had expected and I charged £5. Anyway, I'd like to let him know I'm going to refund but don't want to do it and then have something bad happen* and not be able to refund again if need be.
*I've never had to refund before but there's always a first time, I'm sure.
How should I do it?