Any of the already released version of Excel Connector is fully functional with Jira Cloud, however it is highty advised to use it with the newest available version of the add-in. Important here is to mention that the most crucial thing which differentiates using Excel Connector with Jira Cloud from Jira Server, is how one should log in to get, or to send data back to Jira.
If you try to log in using typical way (login, password and an URL to Jira Cloud), you can expect an error, looking very similar, as the one below:
Check here and learn how to log in via Excel Connector, using the newest and only accepted method for Jira Cloud.