Description

There are cases when the same transition could be run multiple times, for instance, for transitions following re-opening an issue. Or perhaps other processes or users may have already created the issue. If there is a well defined way to know that the desired issue has already been created, then you can use the conditioning support to prevent the creation. For instance, a JQL query can use the your criteria to determine the existence of the issue and the condition can be set to use that information.

See How to create multiple issues - advanced example for techniques to prevent duplication.