Jira issues can be added to a Xebrio milestone. For the specific milestone, click on the External Items tab, click on Link External Items, and choose Jira from the dropdown. Select the Jira issues you would like to add to the Milestone, and then click the Add button. The added issue(s) will now appear in the External Items tab for that milestone.
If the Jira issues do not appear in the list of items to add, please check that the Jira issues has been linked to a Xebrio requirement version. Additionally, Jira issues that were linked to a requirement and then unlinked (removed) from the requirement will still appear in the Tasks module and will still be able to be linked to a milestone.
Depending on a user's project permissions, they may be able to view all the linked Jira issues, or only a subset. Project owners manage the project permissions for users added to the project.