Over a year ago, Twitter announced changes to its API which included the dropping of support for RSS feeds. Version 1 of the Twitter API (Application Programming Interface) was turned off on June 11, 2013. If you were relying on RSS feeds to display your Twitter feed on your website using getFeed or some other tool, it will no longer work.
Twitter does offer the ability to use embedded widgets to display feeds on your website, however, you don't have any control over it—and that's not very MODXy, is it? MODX Ambassador, Jeroen Kenters has written a short guide to get your custom Twitter timeline back on your site using TwitterX and the new Twitter API.