Jira is often used as a project management tool when using Confluence.
So when you create a Gantt Chart, there may be related Jira issues to the Gantt Chart tasks.
Gantt Chart Planner supports Jira integration to make Gantt Chart work with Jira.
Prerequisite to use Jira integration
Application links between your Confluence and Jira that you want to integrate with is required to use the Jira integration feature.
Please refer to https://confluence.atlassian.com/doc/integrating-jira-and-confluence-2825.html to create an application link.