Hello,
We use the latest Jira (7.12.3) with old Confluence (5.3.1). We get an error message "No Confluence page found with the given URL." in mentioned in section (see the image below) and confluence pages have no preview. I added "/display" to Trusted application URL path, but did not help. We have haproxy front of confluence and jira too.

Could you help me, please?
Kind Regards,