Be advised: Epic templates with child issues are available on Easy Templates for Jira Cloud only

Jira Cloud Instructions

You need to have a Jira issue created first so then you can save it as Template

Read how you can define what template fields should be used during new issue creation and what should be ignored using Enabling template fields. Cloud  feature

Be advised that Linked issues are not supported currently and won’t be saved as a part of template.

Check Video

https://www.youtube.com/watch?v=AaCNAomU2fw

Jira Server and Data Center Instructions

Available for Jira Site Admins and Jira Project Admins

You need to have a Jira issue created first so then you can save it as Template

You can choose fields to be saved with Template. While issue creation they will be auto-populated.

KNOWN ISSUE. Jira Server

Template saving may fail for an issue that has a lot of required fields and more than 15 subtasks. Applicable to Jira Server, Data Center instances