I was able to finally buy the product!!!
But I had to figure it out by myself... and try multiple things in order to do it... It is really concerning that we have to do so much work just to get a license you are willing to pay for. If it was some other type of user, less technical, the user would just give up and use another product.
I had to purchase without login into my account, and using PayPal instead (which some other customer may not have). I got the activation key, but when trying to activate, was getting the same 500 error.
I them "purchased" again but using the activation code, honestly I don't even remember all the steps I took, but the server is now activated. This should not be this hard to do.
All I needed was an option to change the payment method in the account menu, something that does not exist.
I got no help from the support... which has an SLA of 24 hours. If it is a Friday, good luck...
You can close this case, I don't want to sound cranky, but the very first experience is not ideal.