At a quick glance, there should be a couple of wires going to ACM and 0V, just on the right of the terminal block. You are quite correct - there is something missing!

You have Mach3 on a PC but how is the PC then connected to the rest of the machine? Likely to be either a simple break-out board connected to a PC parallel port, or a motion control board connected via USB or Ethernet. Knowing what that board is, would help a lot.

There is also an internal parameter setting on the VFD that decides whether the VFD speed is controlled by a control on the front panel or the external input. There might be some other parameters that need setting - there are some cheat-sheets around online that might help. Long time since I configured my own so can't remember what they all are!