Hello
It is not to do with whmcs, look, I paste this link in your vps slider part of the theme:
http://prntscr.com/mzckwo
After I pressed save, in your theme, and go to the front end press vps, and choose for ex the first option (1000) in the slider, and then hover or klick over order button, the link is not correct, it is not the link I pasted in the backend:
http://prntscr.com/mzcm23
If I go down to the price tables on the same page, and hover or click on that button I see/get the correct link. So this means it is some error in the theme.
http://prntscr.com/mzcof3
I hope you understand me better now.
Sincerely
JF