Well I finally managed to purchase the universal bundle this morning. Bank card was still not working but went through using PayPal. I'm never keen on using PayPal but It seemed like I had no choice.
I definitely feel that Serif Affinity should be investigating why there are so many people struggling with this issue. My own thoughts are that whatever payment system they are using is not requesting the correct authorisation from my bank. For me any online transaction needs to be authorised in my banking app and those requests were just not happening.
Check you have the latest browser messaging seems that they want to pass the buck to the customer not themselves. I'd tried with Chrome, Firefox and Edge all on the latest versions, VPN on and off for each and it just wasn't working.
Good luck to everyone else still trying to buy.