Solution

If you already have JIRA Software installed and you would like to install Confluence as well, you cannot install Confluence by way of uploading Confluence installer to JIRA UI.

Confluence is a completely different standalone application/software from JIRA. Unlike JIRA Service Desk which is an extension of the JIRA Software, Confluence cannot be installed automatically from JIRA UI.

The Confluence application:

1. Will be a separate instance from JIRA.
2. Will have its own Tomcat and 
3. Will have its own Installation folders and Home folders in the filesystem.
4. Will need its own separate database
5. Will not be a part of JIRA, however it can be integrated through an Application Link

In order to install Confluence, you would need to install it the way similar that you've installed JIRA. Please find our comprehensive guide regarding this task here:

• Confluence Installation Guide