The PC Move function was available at bungie.net from September 17, 2019 through December 1, 2020. As of 1700 UTC on December 1, 2020 that function was retired and thus no more migrations can be made from Battle.net to Steam.
The best bet is to have your friend return it as the store should not have sold it to them as battle net has not accepted Destiny codes in over a year
English
-
There must be clearly a misscommunication between bungie.net and battle.net since redeeming the code on battle.net worked for me and probably for other people aswell, as long Destiny 2 CDs/Codes are circulating this problem will occur. Taking away the chance to transfer your account from battle.net while still have CDs/Codes circulating with the mentioned instruction to redeem them on battle.net is a scam.