Please follow this guide in your Jira DC instance.
Prerequisite
Please make sure that the server in which your Atlassian products run has access to the following domain: https://login.microsoftonline.com
This is a necessary step in order to validate the SharePoint users that are going to access the SharePoint Connector’s APIs.
Configure Allowlist
In order for SharePoint to communicate with Jira, you need to allow access from the desired SharePoint domain. Please refer to the documentation here on how to do this.
Please use the domain name Expression type with your company’s SharePoint URL, i.e. https://contoso.sharepoint.com.
Please make sure to tick the Allow Incoming option to allow CORS requests
Create application Link
Go to Administration -> Application links and click on Create Link
Create an External application link with Incoming Direction
Configure it as follows
Name: choose any name
Redirect URL: https://<your-jira>/plugins/servlet/senora/redirect
Permission: Write
Save
Configure Connection
Open Manage Apps tab
Open Configure Connection under the SHAREPOINT CONNECTOR FOR JIRA section
Open the Application link configured in the guide above by clicking on the three dots menu and then View Credentials
Copy and paste from the Application Link credentials both the Client ID and Secret in the relative sections
Save