I spoke to MaxCDN support and got this
Queenie L: Unfortunately, the API is no where to be found in the new control panel as it was now removed from the new one.
me: So I can't add any?
Queenie L: Unfortunately, yes.
However the integration will still work even without the API key and ID
me: I use WordPress which relies on the ID though
Queenie L: The API Key and ID is just an optional feature for remote purging of files from the control panel
Will the plugin still work or will it need amending?