The minimum Jira server version Shake correctly works with is Jira Software 8.22. Please update to that —or newer— version to be able to connect your Shake and your Jira server.
If you're running an older Jira server version than 8.22, the solution also exists! We suggest you to use Shake's Zapier integration to forward all the data you want form Shake to Zapier. Then use your Zapier hook to do whatever you want with that data — in your case seamlessly send it to your Jira server version 8.21 or older.