I don't know if there is a group or not for a question like this, but if i buy a s1 license and later want to buy s2 too, do i have to pay for s2 24 pounds or 12? Sorry if it's messy.

Just 12
(PS: it does explain it here https://www.lfs.net/shop as "demo to S1 OR S1 to S2 £12)