PHP Version 5.4.43
After updating to joomla 3.5.1 virtuemart 3.0.16 confirm button no working.
Last virtuemart version is 3.0.0 and new is 3.0.16 confirm of order in paypal payment pro confirm purchase button not working... :-\ :-\
first place to look would be your template
test on the standard protostar template
I had same for a customer, the value are not same in the form,so if you override the cart view in template, you have chance, this not work anymore.
Compare your templates files in \templates\YOURTEMPLATE\html\com_virtuemart\cart\
and Vm file in components\com_virtuemart\views\cart\tmpl\ and check the changes