If none of the above options work, also check your webserver OR cloudfare security settings.
eg Cloudflare might need an IP exclusion for the PC SCM is installed on so that WP remote calls are not blocked automatically.
SCM uses either the WP-JSON or the XMLRPC to upload posts to your blogs.
The XMLRPC is older and by default disabled on most servers.
The WP-JSON is newer but requires you login to your blog and create an Application Password.
We can find solutions to most errors by using WP-JSON first by generating and application password.
If that fails, we can try to install the basic auth plugin.
If that fails, as a last resort we can rename the xmlrpc.php file and use the newly renamed file to post articles.