I've got the latest version of both s2member for wordpress and s2member pro plugin, and all my paypal buttons are suddenly not working, they result in a redirect to paypal with BAD_INPUT_ERROR.
I thought I might need to regenerate the button code, so I tried that and the shortcode is identical, and still doesn't work.
Here is an example page showing the problem (scroll down a bit to see the button):
Nothing has changed on my end since these buttons were working just fine, and looking through this paypal documentation I cannot find the fault: https://www.paypal-knowledge.com/infocenter/index?page=content&id=FAQ2067
Any advice is appreciated.