I just wanted to jump in here and offer something slightly different - praise from an Android user!
This is perhaps surprisingly something I’ve really wanted. Of course, at the moment, I’m happy using Google Pay. However, the addition of Apple Pay is great as I wouldn’t want to be using a bank that I know I wouldn’t be satisfied with if I ever chose to move OS’.
Thanks to the Monzo team for the hard work that I’m sure went into this! 
Bloody good their systems done that so quickly with the refund though. 
Cripes, what are we going to complain about now?! Well done Monzo, and thank you.
I’ve experienced a similar thing at the local pool/snooker hall. Not with Apple Pay, but I’m sure it makes little difference.
Slightly different though, I got the notification on Monzo that the transaction had gone through, but the owner accidentally hit the cancel button on the terminal before it fully completed.
Obviously I told him it appears to have gone through but was happy to go with whatever his receipt said (cancelled) on the assumption that, like most banks, it would reconcile in 3-5 working days.
To my surprise, before the second transaction went through, the first refunded.
So, I believe, it’s just a side effect of the awesomeness of Monzo.
Not sure why it declined on your side the first time, but the whole auth/reconcile/refund process is definitely a refreshing change from legacy banks.
I remember back in the day something similar happening to me in Tesco. Money was certainly not abundant for me at the time and I effectively lost £40 out of my account for the best part of a week. Tesco couldn’t help, NatWest couldn’t help, I just had to wait.
We’re that excited to have you back.
I may also have run into this issue - Apple Pay with Monzo didn’t work but contactless using the Monzo card did, I can’t remember for sure, but I think it was a WorldPay terminal…
Yes exactly same for me, contactless works perfectly well but Apple Pay gave a double low toned beep and just said cancelled on the display.
The Starling card does exactly the same thing!
Yes, I definitely remember the word cancelled appearing when trying to use Apple Pay, so it sounds like exactly the same issue. Perhaps I’ll have to give Starling a go tomorrow to be sure!
Great that Monzo has finally landed Apple Pay! Why is it necessary to ask for a SMS verification code though? Surely your Touch ID or monzo pin would be sufficient.
I also use Starling in-app provisioning Of Apple Pay and it doesn’t ask for a SMS verification code, so it feels more simple to be honest.
Android feature parity (or lack of it!) 
They want to defend against a stolen/compromised device where the app is still logged in but SIM has been removed/cancelled. Not perfect by any means (SMS can be intercepted through other means) but better than nothing.
Tested this out by paying for £50 of petrol at Morrisons and it went through. Awesome! 
Tested Apple Pay today. Made two purchases at Morrisons for £40 and £4.
But none of this transactions appeared in Apple transaction history?
Same for me yesterday, I did use my Watch rather than the iPhone though…
Related:
Strange how the Apple Page has still not been updated to show Monzo…
Also not really seen the Apple Pay release on the usual ‘news’ sites
So happy I can leave the house without my wallet now and have all my cards accessible on my phone! 
Probably because it’s hardly news worthy 
I heard some people were shouting from the rooftops about it…
I would have a response on this but I’m trying not to troll
Yeah it’s not newsworthy now coz everyone has it and no one reports on people that come last in races 
