Help! Why is the Medela hands free pump not working for me?

I’ve been using the spectra S2 with reasonable success for the past 5 months. Able to pump about 5 oz per session when I combine sides. However since I’m going back to work soon I decided to invest in a second pump to keep in the office.

I got the Medela Hands Free free style. I’ve tried it with both the 21 and 24mm shield and both times I was barely able to get a quarter of what I would get in a normal session with the spectra!! Im afraid now that I won’t be able to return this expensive machine and also I’m going to have a hard time continuing to pump when I go back to work. Is there something I’m missing?? Is there a trick to getting this pump to work for people?