There isn’t anything you need to do to use MMR on a subdomain. We do it all the time. There must be something else at play. I would check if there is a conflict with another plugin and try a different theme. Do you have any error messages?
The message is “No files have been processed”.
I only have 1 plugin installed that is Polylang. Could be the home URL of the site? It is sample.com/es/ or sample.com/en/ not sample.com/.
The theme is a theme that I developed, and with this theme I have other domines that this plugin works perfectly but in any of them I have Polylang installed. It could be the problem…
Ok, I have tried in another subdomain that I have without Polylang and does not work too. Is not this plugin. And I does not have any other plugin installed.
My subdomain URL is https://subdomain.domain.com/ there is a problem with this structure?
I do not know what is happening…
Any chance you can grant me access to have a look? You can contact me here: https://launchinteractive.com.au/enquiry
