Upcloud manual activation?

So today I decided to register for Upcloud and I created an account. However, I received an email from their support team telling me that activation was not successful for "reasons they cannot disclose" and they asked for my info and a photo of my card through email!!
I tried to know what their reasons were but they insisted on not telling me. In the end, I told them that I don't feel safe to share such information via email.

Anybody understands why that might be?