If you are having trouble connecting to your TypePad.com blog, it may be due to a change in TypePad’s server policy for connections to its API (the interface that apps like MarsEdit connect to).
Starting in late 2018, TypePad has apparently started requiring that all connections be made over “HTTPS” the encrypted version of the HTTP protocol that web sites use. If you have previously configured a connection to your TypePad blog using a “HTTP” based URL, then the connection may suddenly stop working.
The solution is simply to open the settings for your blog in MarsEdit’s preferences, and change the “Home Page” and “API Endpoint” URLs to use “https://” instead of “http://”. After making this change you should be able to connect again to your TypePad blog.