I have exhausted all my checks and read all relevant community and support tickets.
The Confluence Jira Macro does not work properly in my setup. I can open the dialog but can neither search nor create Jira Issues from Confluence (see error msg in post title).
Application Link is set up correctly both ways with OAuth enabled and working properly. I am successfully using Jira user directory to authenticate in Confluence (Jira is primary user directory). Collaborative editing works fine.
Confluences Spaces are connected to Jira Projects in Space configuration. Users have correct roles in Jira and Confluence.
All Jira related system plugins are enabled in Confluence.
Both Jira Core and Confluence are installed on the same Windows VM. Connection is routed over SSL thru an IIS Proxy. Certificates are valid. No other issues on either Application.
Base URLs are: https://jira.<mydomain>.com and https://wiki.<mydomain>.com
Browser Console (Chrome) shows http 400 error (bad request) on URL:
https://wiki.<mydomain>.com/plugins/servlet/applinks/proxy?_=...
https://wiki.<mydomain>.com/s/.../_/download/contextbatch/js/editor-v4,atl.general,editor,macro-browser,page,main,-_super/batch.js?frontend.editor.v4=true&healthcheck-resources=true&hostenabled=true&locale=en-GB&whisper-enabled=true
When I try this URL in a separate browser window, I get java.lang.NullPointerException
at com.atlassian.confluence.plugins.jira.AppLinksProxyRequestServlet.doProxy(AppLinksProxyRequestServlet.java:60)
A problem with the IIS reverse Proxy? I checked SSL Configuration in IIS and noticed, that the Jira Application was not configured to accept client certificates. So I switched that option on. This resulted in the Jira Macro to show the Create Issue dialogue - but only once. The fields where read-only. Since then, same behaviour as before.
I checked the http request parameter length in the Windows registry which was described in another thread as a possible issue. It is 4096 in length and therefore probably no issue here.
Confluence is v6.15.4 and Jira Core is v8.3.2
Any ideas are much appreciated. Thanks.