Problem to unlock Pro version on mobile

I subscribed to Secure Browse Pro for five devices. On my PC, all is fine. But on my mobile, there is no way to activate it, and it only allows me to use the free version.
I have an activation code and there is not way to enter it. It also does not activate PRO when I log in with my Avast account.
Suggestions. ???
Thanks

Hi Caruso.

Please can you provide me more details about the mobile browser. What system do you use?