If you want to sync a number of units to MIDIclock, there are a couple of things to check. See UM for explanations.
Firstly, the first unit must be set to OUTPUT=XMT and MIDICLK OUT = ON. This allows it to generate and transmit its MIDIclock tempo.
Subsequent units must be set to MIDICLK IN = ON (to receive MIDIclock) and OUTPUT = THRU (to pass the received MIDIclock through to the next one).
That should do it.