You make the refund in GoCardless, not here. That is where your money is, and where sending it back belongs.
What this does is make your club's own record agree with your bank afterwards.
Matching one up
We hear about a refund the moment you make it. It appears on the Money screen under Refunds you have made, with the household, the amount and the day you sent it.
Press Match this refund. The reversing entry goes on that member's record and their subscription goes back to owed, for the amount you sent back.
No amount is typed anywhere, by you or by us. A figure typed twice is a figure that can disagree with the bank.
Until you match it, nothing on the member's record has changed. That is deliberate: a refund can be a correction, a leaver or a gesture, and only the club knows which.
What it looks like afterwards
The member's record shows the payment and the reversal, both dated. The payment does not quietly disappear.
So a year later somebody can read what happened, instead of finding a gap.
Or did they never owe it?
That is a different answer. Waiving the sub is the one for a committee decision rather than a bank transaction.