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Logical operators, Functions and operators are same as the JQL in JIRA. It is important to use correct JQL syntax.
The easiest way to write a JQL query for JSU is to prepare it first in Jira's standard search interface (use 'advanced search'!) with some sample value. Then copy it to JSU configuration and replace some of your sample values with {issue.FIELD NAME}s as required.
Think careful about what might be the result of your query
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If you have severl custom fields with the same name, you must use the custom field id.
Troubleshooting
In general it's a good idea to check your log files about any errors and warnings from JSU. Even more when you're using complex JQL queries in JSU.
While you configure a new workflow with JQL queries in JSU, you might even set the log level to DEBUG for the following package:
ch.beecom.jira.jsu.util.jqlSee also Troubleshooting how to change a log level.