I have 12 sites on a WordPress multisite installation using the subfolder format i.e. www.mydomain/site2

I am trying to add pages and contact forms from one subfolder site to another subfolder site so I am trying to export the pages and the contact forms in two separate exports. I do not want to export the entire site.

After I select either the pages or contact forms to export, I get a 403 nginx error.

How do I overcome this issue please?