Funds transfer authorization
_debitBalanceAmount = debitBalance;


Assigning this to a member value doesn't seem right, and this is before any validation.

GetFundAmountToTransfer();


This function is implies it will return something, but you don't assign it anywhere.  This is a code smell.

var result = GetProceedInstruction();
if (result == "1")
    return _callerAuthorization;


A meaningless string literal, not good.  Make it an enum with a good name.  Where did _callerAuthorization get assigned?

The control flow is not complicated and yet it's hard to read.  Try breaking it up into smaller functions.