All VFD have screw terminals where they have relay contactor that switches on or off when the spindle motor is powered or not. Read the manual.

From there you take 2 wires and wire them splitting the line of the big red button saying Estop. Read the BOB manual and be careful not to split 220VAC, cause some Estop buttons have double chain, one for the small voltage signals/5-24VDC depending on the BOB/ and one for directly cutting the 220VDC power/mine for example is made like that/