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Based on changed APIs by Atlassian, external gadgets are no longer supported. In consequence of thisConsequently, the approach described below no longer works, and traffic-light fields' content will not be rendered properly.
Instead, you can use my app "Integration of Jira fields into Confluence" (https://marketplace.atlassian.com/apps/1221429).
Beside rendering of : since 2021, this app is archived on the Atlassian Marketplace and no longer available for installing due to economic reasons.
Nevertheless, you can install this app manually: 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. This version is free of charge and unsupported at your own risk!
Besides rendering Jira fields including Traffic-Lights, you have also the advantage of specifying a Time Machine to use the field values as of <date/time>:
that's really helpful in case of e.g. reporting to always display the same historic value for a given timestamp.
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