Why doesn't the cash drawer open?

Install the driver in your computer and connect with cash drawer port, as below.

For Windows: Change the option follow the path：Start---Settings---Printers---POS-80C---Manage---Printing preferences---Printer settings---cash drawer

Figure 1 Cash Drawer Setting

For Mac: In the printer features, choose “Cash Drawer Control”, select “Cash Drawer 1 Before Printing or After Printing”.

Figure 2 Cash Drawer Setting