Callout logs are accessible from the Salesforce App Launcher:
- Go to Salesforce App Launcher, search for and click REST Callout Logs.
- Use All, Failed or other appropriate list views (Nextian add-ons will usually add their own, application specific list views).
- Open a record to access all details.
and Nextian settings:
- Go to App Launcher → Nextian Settings.
- Navigate to the Rest Callout Logging tab.
- Click Open Callout Logs button.