Will MainWP work with Wordpress on C9.io?



I’ve created my first Wordpress site, and added MainWP child to it.

However, when my MainWP Dashboard site tries to connect to my child site (https://custom-theme-stevedoig.c9users.io/), it replies with the error:

MainWP Child Plugin not detected, first install and activate the MainWP Child plugin and add your site to MainWP Dashboard afterwards. Click here to install MainWP plugin (do not forget to activate it after installation).
Hint: On your child site, go to the Server Information page and verify that the SSL extension is enabled.

Help appreciated.