in the connections "gable end plate", "moment end plate" and "simple side end plate" you can select slotted part.
you also can choose between plate, beam or both.
but you need to have the plate slot horizontal and the beam vertical or visa versa.
never in the same direction.
Because this is part of the connection you can't do the slotting afterwarts by selecting the bold parameters.
so the connections should have an update and slot both ways or the slotting should been trown out of the connection.