Enter App name and select Development Slack Workspace. App name can be anything and by default Slack Workspace is Group but you can sign in to another workspace.
Click On Create App.
Scroll down on page and copy Client ID and Client Secret, keep it handy for setting up Jira as OAuth Client later.
Add Redirect URL : Go to OAuth & Permissions, click on Add New Redirect URL button.
Provide the Callback URL (copied from plugin) in the given text field and then click on Save URLs.
Scope: In the same OAuth & Permissions page, scroll down to the Scopes section.
Click on the Add an OAuth Scope button under User Token Scopes section. Select appropriate scopes from the dropdown list and Save changes. E.g. identity.basic and identity.email are required scopes.