Hey there, Alan.
From the plugin page itself (https://marketplace.atlassian.com/plugins/burn-up-chart), we can see that the last supported version of JIRA is 6.1.7. So, I think that the best thing to do is to contact the plugin vendor to confirm with them whether there are any plans on providing this plugin for later versions of JIRA including 6.2.1.
Perhaps you can drop them an email or give them a call for a quick clarification. Good luck!
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