Thank you for your reply, @Jineet_Vora. I'm using the RESTClient plugin for Firefox. That addon helpfully outputs the equivalent `curl` command for the requests it sends. The curl command it provides in this case is:curl -X POST -H 'Authorization: Basic XXXXXX' -i 'http://test-aem.company.com:4502/b...

I'm following the instructions for upgrading to XML Doc 4.0, and when I get to the point of doing the POST to /bin/dxml/upgrade/3xto4x I get a "403 Forbidden" response. My GET to /bin/dxml/upgrade/3xto4x/report worked fine, and the report included: "upgradeStatus": {"status": "MIGRATION_POSSIBLE","m...