Enable Cross-Origin Resource Sharing (CORS)
Enable Cross-Origin Resource Sharing (CORS) on your Acrolinx core server. Check out this article on how to enable CORS.
Secure Acrolinx with SSL
Make sure that your Acrolinx core server is secured with SSL, because Acrolinx for Office Online only connects to Acrolinx using HTTPS. This means that your Acrolinx URL in the Sidebar has to start with the prefix
https and follow this pattern: