It might be your internet connection, an Adobe server going down, your credit card's server going down or maybe even someone is staying home for the pandemic this week.
What have you tried? Where are you trying to buy? How many times have you tried? Do you have to have it right now? Have you downloaded the trial? Are you haveing a bad day? Who sent you the email? Have you tried https://helpx.adobe.com/support.html
So, I have tried to buy online twice and the purchase has been rejected twice. I am an American living in Germany. I do not have any problems buying software from any other vendor, but I suspect Adobe has implemented something idiotic into their purchasing process. I will call them tomorrow to find out WFT is going on.
Try the German version on a free trial. It is the same. At install, you pick your language. If it works buy a serial number. If you are trying to buy from a USA site and you're in Germany, it might have a lot more to do with EULA, regulations, taxes and international relations than any stupidity at Adobe.
Please consider installing a trial before you spend real money.