func: function increaseApproval(address _spender, uint _addedValue) public returns (bool){
          
          require(_spender != address(0), "Address is wrong");
          require(allowed[msg.sender][_spender] > 0, "Not approved until yet");
  
          
          require(!blackList[msg.sender], "Sender in blacklist");
          require(!blackList[_spender], "Receiver in blacklist");
  
          uint oldValue = allowed[msg.sender][_spender];
          require(_addedValue + oldValue <= balanceValue[msg.sender].unlocked, "Unsufficient balance");
  
          allowed[msg.sender][_spender] = _addedValue + oldValue;
          emit Approval(msg.sender, _spender, allowed[msg.sender][_spender]);
          return true;
      }