Installing apps directly from Atlassian Marketplace (since 2021: no longer supported because archived on the Atlassian Marketplace due to economic reasons)
Installing by file upload (not having direct internet access): download the app from my server at https://polscheit.de/plugins/jira/jiraFieldsInConfluence/jiraFieldsInConfluence-1.0.0_free_unsupported.jar and install this JAR file via the button "upload" on your Confluence page "manage apps" as a system admin.
Then, create AppLinks between your Confluence and your Jira. That’s a prerequisite for requesting data from Jira by Confluence.
If you have any questionquestions, please do not hesitate to contact me at support@email@example.com