Battle.net desktop app, Windows 10 PC. I have experienced repeated failures during the payment process for £9.99 one-month subscriptions, both this month and last month. The process often fails mid-way, or puts me through to a confirmation screen requesting my expiry and CVV, where the ‘Subscribe’ button never becomes interactable, essentially bricking the transaction.
Usually after closing and re-opening the bnet app 3-4 times this tends to resolve itself.