This is from our new tech contact at Ingenico:
it looks like your system was trying to access the Connect HostedCheckout page without the HostedCheckout ID. For instance, every time yours system submits a new CreateHostedCheckout API, you will get a unique redirect URL which looks similar to
but it looks like sometimes your system will just put 'https://payment.pay2.secured-by-ingenico.com/checkout' in the iframe which had triggered a lot of the errors that we are seeing. Can you ask your development team to double check on this?
Let's start with a bunch of logging at least.