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Due to major implementations on Security and Encryption for Confluence & Data Center, if you are upgrading from an older version of the app, it is recommended to following follow the upgrade path provided below.
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Before upgrading each app ensure you update Confluence
go to Administration > Plugins Apps > Manage Existing.
disable the Security and Encryption for Confluence & Data Center app
update Confluence
After upgrading Confluence, update Security and Encryption for Confluence & Data
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Center
Administration > Plugins Apps > Upgrade
enable the Security and Encryption for Confluence & Data Center app