Atlassian Marketplace no longer displayed

[Alan Cross]

After a manual rollback from a failed JIRA Core upgrade, I restored the previous version of JIRA (from v7.4.2 to v6.1.7), but when trying to check add-ons, the Marketplace does not show making it impossible to manage add-ons. I cannot find anywhere how to reinstall this or even if it is possible. Have I done somethign wrong during the rollback?

[Nic Brough -Adaptavist-]

AS discussed at https://community.atlassian.com/t5/Jira-Core-questions/Issues-created-after-upgrade-still-displaying-after-manual/qaq-p/648708 , I think you have broken your system with a partial roll-back.