Mrp Blog Problems creating new posts using WordPress 5.2.3

I recently tried to post a blog entry after upgrading WordPress from v4 to v5 and discovered that I couldn’t save a draft or publish it. The diagnostic in the console wasn’t all that helpful to me. Entries such as Cross-Origin Request Blocked: The Same Origin Policy disallows reading the remote resource at https://www.mrp.net/blog/index.php?rest_route=%2Fwp%2Fv2%2Fposts%2F255&_locale=user. (Reason: […]