Email distribution web service piped text not working

I have the following text in a test email distribution
Test web service -- ${ws://WebService?u=http%3A%2F%2Fecho.jsontest.com%2Fkey%2Fvalue%2Fone%2Ftwo&f=one}
The URL http://echo.jsontest.com/key/value/one/two returns JSON that Qualtrics recognizes when I use the 'Piped Text from a Web Service' option within the email distribution editor, however the email that is sent only contains
Test web service --
Has anyone else had any luck getting the web service output in an email distribution?