Trying to get FFT output to ZMQ

I am trying to recreate an equivalent to the QT GUI Frequency Sink to output over ZMQ so I can receive values in my own code. I am running into a snag. I tried to follow what was shown in the FFT docs (see my flowgraph for ch0, compared to the one from I can’t get anything but ~0 as the output from the FFT. In fact, what is quite strange is the FFT ALWAYS has the exact same output. Something seems quite wrong, considering I get normal noisy output from the GUI sink.