RpcResponseException: Invalid parameters: must provide an Ethereum address.: eth_sendTransaction

i can’t get metamask to work for transactions on mobile i alway get this error

    public async void SendERC20(int amount = 20)
    {
        MoralisInterface.InsertContractInstance("transfer", ABI, chainId, "0xDFC32b0128341Ce7e8835e2Af563f62ba738F960");
        BigInteger cost = new BigInteger(1000000000000000000);
        string fromAddress = "0x7C7605045f8Da27010Ec60c0e192E558a1F3a2c4";
        var user = await MoralisInterface.GetUserAsync();
        string receiver = user.accounts[0];
        Function f = MoralisInterface.EvmContractFunctionInstance("transfer", chainId, "transfer");
        HexBigInteger gas = new HexBigInteger(80000);
        string result = await f.SendTransactionAsync(fromAddress, gas, new HexBigInteger("0x0"), receiver, cost);
        Debug.Log(result);

    }       

what error do you get? this is in Unity?