Configure Okta Token.

On updating token details, Click Test Connection.

See, Okta API Token Help

Choose remote user directory as Okta.

Configure Manage Former Users form.

To Debug Manage Inactive Users App:

Go to System General Configuration > Logging and profiling > Default Loggers > Click Configure.

Class/Package Name: com.tse.jira.deactivateusers.plugin
Level: Debug