Follow the instructions in this document to reset the stock units from negative to zero

Negative units are created when you bill an out-of-stock item. Refer to the image below:

Procedure:

1. Open MySQL command prompt (Windows), mysql -u root -p from root (Raspberry)
2. Password is password
3. Type
   
   use SALECULATOR;
   
   And press the Enter Key
4. From the MySQL command prompt type the below query
   
   UPDATE STOCKCURRENT SET UNITS=0;
   
   And press the Enter Key
5. Type exit and press the Enter Key

6. Restart the system and check the inventory now