Shortcuts I had on some mouse buttons didn't work today. It seems Keyboard Maestro doesn't register device keys any more.
I've checked it in other software (karabiner, steermouse) and the keys are definitely working.
So I just thought fuck it... I'll upgrade KM from 9.2 to 10, maybe that will fix it.
But when I click on the button to confirm the order, I'm being told:
Do you hide site elements e.g. by using ublock origin or some other adblocker?
When I open the page to purchase a license I have the same view like you, but then a section with billing information follows and lastly a line with a check box and the terms and conditions, just before the button to finalise the order.
Do you see the same problem on the standard "get a new licence" page, or is it only happening for an upgrade? See if you can tick the box before applying your upgrade coupon and entering payment details.