Sophos XG86 license ?

Only from a reseller. Sophos is a Channel only business.

But there are reseller, offering the license on a website. Watch out by purchasing, you are currently purchasing from a official Sophos reseller and not a third party. 

You can verify it here: partners.sophos.com/.../

Why I cant buy from non-official seller? My official reseller is on vacation.

It is against the EULA. https://www.sophos.com/en-us/legal/sophos-end-user-terms-of-use

And how this prevents using license?

And how this prevents using license?