Everything in one place
Your agreed swap, the requests you've sent, the ones waiting on you, and how your listing looks to everyone else.
If something goes wrong on the call
They didn't answer when DVSA rang
The swap doesn't happen and nothing is spent. DVSA calls the number registered to their booking, so if they've changed phones recently, that's usually the reason. Agree a new time and try again.
One of us failed the security check
Both tests stay as they are. Have your licence number and booking reference in front of you before you ring, and make sure the details you give match what's on the booking exactly.
They changed their mind on the phone
That's their right, and no change is spent by either of you. It's the main reason to message properly before you call rather than arranging a swap with someone who's gone quiet.
DVSA said we'd run out of changes
One of you has already moved the booking twice. There's no way around it. A third change cancels the booking rather than moving it. Check on GOV.UK before you agree a swap, not after.
We're inside 10 working days now
Then it's too late for this pairing. The clock runs to whichever of the two tests is first, and Sundays and bank holidays don't count towards it. Both of you should relist. There'll be other matches.
I didn't get a confirmation email
You won't. DVSA doesn't send one after a swap. The next reminder email about your test will show the new details. If you want to check sooner, sign in to your booking on GOV.UK.