I don’t know if this is specific to my setup, but after deploying Let’s Encrypt certificates to my Azure App Service hosted site, I had a problem with Windows Live Writer and the metaweblog.axd endpoint.
I had to manually edit the settings.xml file found in App_Data. At the bottom of the file, look for
And set it to True
To be safe I restarted the site, and after that, no more problems posting to my SSL based site from Live Writer.