Can’t subscribe to RSS on iOS + Downcast

Running iOS 10.2.1 and Downcast 2.9.16.6127. Having problems subscribing to the premium RSS, getting “authentication failed” errors.

Originally I was using a long password with special characters. Saw that that could cause problems, so I switched to alphanumeric only and confirmed the new password works logging into the website. Also tried inlining the username and password in the URL. Unfortunately still getting authentication errors in Downcast.

Thanks in advance.