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Click on the gear settings icon inside the Jawaker application. You will find the "Player Number", copy the ID. Go to www.jawaker.com/en/code and enter the ID and the code then click on Submit.
LOGIN TO YOUR STEAM ACCOUNT, CLICK ON YOUR ACCOUNT NAME -> ACCOUNT DETAILS -> ADD FUNDS TO YOUR STEAM WALLET -> REDEEM A STEAM WALLET CODE
Launch the League of Legends client. Click on Store -> Purchase RP -> Prepaid Cards & Riot Pin and enter your code.