This would be better placed in the ITOM Forum in the future, as it relates to Discovery.
Basically - the error message indicates to you that the SSH Credentials on the platform are not sufficient to allow access to the targeted hosts. In fact there should be a pane on the right of your screen advising you on the appropriate next steps.
I recommend you complete (if you haven't already) the Discovery Fundamentals on demand:
https://learning.servicenow.com/lxp/en/it-operations-management/discovery-fundamentals-on-demand?id=...
And of course, the Product documentation spells out the commands requiring privileged user(s) so you are able to work with infrastructure teams to deploy SSH credentials & sudo configs.
Hope that helps!
Sam
