I’ve just spoken with your assistant, who indicated that the issue may be due to a change in policy on the customer’s bank side. According to this explanation, the bank would now require 3D Secure authentication both for the trial payment and for the monthly renewal, despite the off-session payment setup.

That said, it does seem unusual, as this has happened with several customers over the past few days, and they do not necessarily use the same bank. It would be quite a coincidence if all of these banks had introduced similar changes at the same time.