This is how you set stock to negative in RSA,
Go to Manage mode in RSA
Select PLUs
Search for the product by name or PLU that you are trying to change
Find the Stock on Hand (SOH) section
Select the SOH box and a pop up box will appear
In the pop up box, a negative symbol (-) is first put in.
the amount of stock that is be put in needs to be put in as single units, Eg for 2 cases(of 24) and 1 bottle, -49 units needs to be inputted
Press enter