Welcome back to Allods
Subscription is purchased using blue-crystals (not actual money, unless you intend to buy the crystals with money -- in which case the end result is the same), thus we don't have subscription/steam wallet functionality at this time. Having subscription tied to blue crystals allows players to purchase subscription via in-game means, leftover crystals from purchases, or simply buy it outright by purchasing the required amount of crystals needed to subscribe for the chosen length of time.
Given lack of account linking between steam and non-steam accounts, it would be safer overall for purchases to be performed on-site even if the feature existed. Steam is new territory for us and no doubt we'll be improving things over time in various ways, but for now it is not possible.
Regards,
Mhul