We have setup 2 Jira Installations, one Jira Service Desk on Host A and Jira Software on Host B. Both applications are linked bidirectional to each other. We are able to link an issue in Jira Service Desk to an existing ticket in Jira Software. The status of the linked issue is also updated, so i think the application link is configured in the right way.
Creating a Link:

But when we want to create a linked issue in Jira Software we are not able to choose the Jira Software project. Only the Jira Service Desk project could be choosen to create an issue.
Create a linked Issue:
What have we to configure to get this function work?
Best regards
Joerg