How can I disable a la carte purchases for students who have a negative balance?

To disable a la carte permissions for students who have a negative balance log in to the LCS1000>Lines tab>Lines Setting.

Select the serving line by clicking on it.

Click on Line Settings. 

Click the Edit button. Toggle the "Disable A La Carte Below Threshold" setting to "Yes" and enter the threshold amount, as seen on this example:

Click the "Save" button.

This setting is line specific so you will need to repeat these steps for all of your serving lines, if necessary.  When a student with a balance at or below the threshold goes through this serving line, a la carte items will not be displayed at the point of sale and thus cannot be sold.