Whatsapp more than a year subscription not working?

I would like to pay for 3 or 5 years, not just one: I send to myself a payment link from the app, but link in paypal only offers 1 year subscription?

Googling, I find that
http://dayures.blogspot.com.es/2013/06/very-easy-how-to-pay-whatsapp-using.html

And information is correct: md5sum in the url is as link describes, but changing sku=3 or sku=5 does not change nothing ?

I have no idea how to solve it ...