The on platform ticket machines won’t accept Monzo cards. It always declines in the machine, in app it shows as pending and then reverts 7 days later. I’m not sure why it does this but I’ve had the issue in London Kings Cross, Leeds and Newcastle stations.
It may be worth emailing email@example.com from the email account linked to your monzo and give them details to investigate.
Thanks will do! It’s really odd as I can use curve linked to Monzo in the machine. So it must be a basic issue somewhere. Have emailed.