I have installed (multiple times) MainWP Child plugin Version 18.104.22.168 on a subdomain (https://islandsmiles.bytique.com) running Wordpress Version 5.7.2. The plugin fails to activate (both in Installed Plugins and from WordPress.org/plugins) and MainWP Dashboard Version 4.1.6 does not recognize the MainWP Child site.
I have disabled all other plugins and cleared cache, uninstalled and re-installed the MainWP Child plugin without activation.
I have installed multiple MainWP Child plugins on other sites and had them recognized by MainWP Dashboard without problem.
Are subdomains accepted?