To open an URL from your zendesk ticket sidebar you can configure the Deeplinks App URL like this:
- let's assume you have a JIRA-ticket ID stored in a custom field with the ID 3600000999
- deeplink configuration
- https://<yourjirainstance>.atlassian.net/browse/{{ticket.customfield_3600000999}}
Please find a list of Placeholders with examples here:
Deeplinks App - Example placeholder list