Validate that All Mandatory Items are Complete
This rule blocks a transition unless all mandatory checklist items, including items on both Local and Global Checklists are complete.
This validation rule only works in Company-managed spaces.
To set the workflow validator:
Navigate to Space settings > Workflows
Click Edit workflow.

Select the transition where you want to add the rule and click on the Rules + sign.

Click on Checklists for Jira under Marketplace Rules and select All mandatory items are completed.

Click Select.
Click Add.

Click Update workflow to save the changes.

Troubleshooting Validators
Checklists for Jira uses work item entity properties to provide the following features:
Therefore, the Checklist must be able to set work item entity properties. This is enabled by default. However, if a jira.permission.* workflow property has been set on a workflow step, Checklists may not be able to set issue entity property.
For example, the following property will prevent Checklists from setting work item properties, and features listed above won't work correctly:

Removing the jira.permission.* workflow property and using the standard Jira permissions to control who can edit the work item will allow the Checklist functions to work.