To get Gantt Chart to work you need add a custom field named Issue Start Date on administration backend and confirgure it your projects on JIRA.
Adding a Custom Field Step by Step
First go to Issue Custom Fields in administration backend.
Second select a Advanced and find Issue Start Date.
Fourth select all project checkboxes.
You are done if you see Issue Start Date custom field on all your projects.
Configure custom issue linking
|Name||Outward Description||Inward Description|
|Finish-to-Finish||FF-depends on||is FF-depended by|
|Finish-to-Start||FS-depends on||is FS-depended by|
|Start-to-Finish||SF-depends on||is SF-depended by|
|Start-to-Start||SS-depends on||is SS-depended by|