The Expressions page enables users to define custom logic for workflow validators, conditions.
Add New Expression
Click on the "Add Validator" button.
Select the ‘Custom Expression Validator’.
Click on Add button.
Provide the required values in the text field
Provide an optional title for your validator.
Enter the Jira expression for the validator.
Type the error message to display if the Jira expression returns false.
Help Button
Click on the Help icon at the Top right to see the Help links.
Mapping expressions allow users to create dynamic expressions that can be applied to various Jira fields during issue transitions.