When want to add a new child site, I enter the domain name and press Test Connection. Nothing happens, but in the browser console the following error shows up:
Uncaught ReferenceError: with_www is not defined at mainwp_managesites_test (mainwp.js:1686:5) at HTMLInputElement.<anonymous> (mainwp.js:1889:5) at HTMLDocument.dispatch (load-scripts.php?c=0&load[chunk_0]=jquery-core,jquery-migrate,utils,regenerator-runtime,wp-polyfill,wp-hooks,heartbeat,zxcvbn-async&ver=1fa15bd54f1ffa3deb2eeb20afdc3d39:2:43064) at HTMLDocument.v.handle (load-scripts.php?c=0&load[chunk_0]=jquery-core,jquery-migrate,utils,regenerator-runtime,wp-polyfill,wp-hooks,heartbeat,zxcvbn-async&ver=1fa15bd54f1ffa3deb2eeb20afdc3d39:2:41048)
When I actually add the site, it works so the issue is limited to testing the connection.