Can't trade gift cards, but this will work for OSRS too since if you get membership on one you get it on both games :)
ahh i didnt know that was against the rules! my bad. i will close the thread but i tried for like 45 minutes to find a way to apply the card to my OSRS account but it wont let me.
when i go to the redemption page on Jagex's website and enter the code it says "Sorry, Pre-Paid Cards cannot be used to extend your active membership subscription." then it says:
Please select which package you would like to redeem this code against:
44 Keys
265 RuneCoins and 25 Keys
570 RuneCoins
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i put a support ticket in to Jagex to see if there is anything they can do but before i bought the card i searched online to see if i could use it for OSRS and not just RS3 and like you said.. everything i saw said i could apply it towards OSRS or RS3.
i dont know why a gift card isnt acceptable for Membership Payments, but if i cant "convert" it to OSRS then its useless. just a wasted 25 bucks..