MIDI CC Controller not working with Pro Tools and Serum

I'm able to use MIDI learn to map a controller knob from my Arturia Keystep 37, but for some reason it won't actually control the knob. For example, I'm trying to map the controller knob 1 on my Keystep to the filter cutoff; even though it maps the CC I'm still unable to use that knob to control the parameter. Is there anything else I need to do to get this working?

I would recommend making sure the CC is transmitting on MIDI CH 1. You could try drawing a MIDI CC as automation on the track itself, and see if that works.