item should be sold in multiple of 6

Summary: item should be sold in multiple of 6

Content (required):

Item is manufactured and stored by unit of Ea. But should be sold in multiple of 6.

How should I avoid users to enter qty that are not multiple of 6 for specific items?

Version (include the version you are using, if applicable):

23C

Code Snippet (add any code snippets that support your topic, if applicable):