Problems opening cash drawers are usually caused by an issue with the printer the drawer is hooked up to.
The following are common troubleshoots for this problem:
Customer Receipt Printer: Make sure you have the correct receipt printer selected by going to the "Device Center" and clicking "Print Settings" > "Customer Receipt Printer". Click on customer receipt printer and select the correct printer associated with your cash drawer.
Verify that the printer wired to the cash drawer has paper and is powered on with no error lights
User Permissions: Verify the employee pinned into the system is setup with a role that has the permission to access the cash drawer. Learn more about roles here.
Locked Drawers: Make sure the cash drawer is not locked
Connector Cable: Ensure the cable connecting your cash drawer to your printer is plugged in securely on the right ends. Read the hardware setup guide for more info on how to connect the cash drawer to your receipt printer.
Verify you are using the correct cash drawer cable for your model of printer. (Epson cables do not work with Star printers, and vice versa.)