Why can't I create knowledge base link between JSM and Confluence

Question

I'm a site admin of our Jira/JSM/Confluence and I have administrative permissions for a JSM project and confluence space. I try to link the confluence space as a knowledge base to my JSM project, but the linking fails (HTTP 403). The only error message I can see is "We couldn't link the space 'XYZ'
 refresh the page and try again"

The global permissions of Confluence are set to allow JSM user to use confluence and view user profile.

Is there something I'm missing here? I have tried to Google the issue and to see instruction articles but without success...

Edit:

Also I'm unable to create a Confluence space from JSM side, but from Confluence I have no issues. When I try to create a space from JSM project settings, I get follwing error:

However, Confluence is not down or my permissions (as a site admin with full privileges) shouldn't be the issue.

Callum Carlile _Automation Consultants_ · Answer

@Jussi Sarén I'm glad you've got it all sorted! :)

Jussi Sarén · Answer

We got this issue solved with Atlassian support. There was a permission issue. My JSM project's permission set didn't grant "Service Project Agent" permission to our "Administrators" group and that was the issue. The need of this permission (even if it's now obvious) wasn't mentioned in the step-by-step guide and therefore I wasn't able to self-diagnose this by myself. However I requested Atlassian to update the instuctions so that the demand of  the permission would be mentioned.

Jussi Sarén · Answer

@Callum Carlile _Automation Consultants_  yes. I belong into administrators group which has both, create space and personal space permissions. I have also created spaces directly in Confluence lately so that shouldn't be the issue. Maybe I'm going to raise a support request.