The most common error a vending machine has is an understock error: error 34. A customer will select a slot, and the slot will give an "out of stock" message and not vend. If there is product in the slot the customer selected, this can make them upset and hurt business. This guide will walk through what causes understock errors as well as how to fix them.

To check if a machine currently has any understock errors and clear out any that exist, follow these steps:

1. Log in to the service menu of the machine.
   
   
2. Using the arrows on the keypad, navigate down to the Clear Slot Error option and hit the ENTER key.
   
   
3. A popup box will appear and begin counting down from 3 seconds. There are two options from this point:
4. 1. If ENTER is pressed before the timer counts down to 0, all slot errors will be cleared, including understock errors.
   2. If the timer counts down to 0, a new popup box will appear listing any slots with errors as well as what error the slot is experiencing. Pressing ENTER on a slot in this menu will clear any slot errors on that slot, including an understock error. Hit ENTER on every slot in this menu.
      
      
5. While the machine is clearing any slot faults, it will display a message stating "Clearing..." Ensure that the message becomes "Clearing...Succeed" before moving forward.
6. 1. Note that when an error is cleared from a slot, the slot may rotate to fix its home position. Be ready to catch any product that may fall!
      
      
7. If any complaints were received or slot errors observed on any specific slot(s), close the machine and select those slot(s) as a customer to ensure the understock error does not appear again.