Paralax Slider Activation

When I try to activate the layer slider plugin I keep getting the message:

“Your purchase code appears to be invalid. Please take special care to enter it correctly without accidentally including spaces or other additional characters. Please note, this feature won’t accept your theme’s purchase code. This also can be a temporary issue in our services. In that case please try it again in a few hours.”

I have tried multiple times and the same thing always happens