Structure of a matchmaking system

General
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6

I tried your suggested algorithm and got the following error on localPut when i call the smart contract for second player (Bob):
logic eval error: invalid Account reference
Here’s the code (I wrote a comment where I received the error):

      scratchWaitinglayer.store(App.globalGet(Bytes("waitingPlayer"))),
        If(scratchWaitinglayer.load() == Bytes(""),  # no player in Queue
           Seq([
               App.globalPut(Bytes("waitingPlayer"), Txn.sender()),
           ])
           ,  # a player is in Queue
           Seq([
               App.localPut(Int(0), Bytes("partner"), scratchWaitinglayer.load()), #Got error here
               App.localPut(scratchWaitinglayer.load(),Bytes("partner"),Txn.sender()),
               App.globalPut(Bytes("waitingPlayer"), Bytes("")),
           ])
           ),