I posted this diagram above, but take a look. This is for three Inovellis, where the middle and right are powered by a hot and a neutral. So as is in the diagram, there is a hot and neutral in each box.
So the only thing you change is to swap out the middle switch for an Aux to make it and the left switch into a 3-way. Aux switches only need two conductors between it and the Inovelli. So between the left Inovelli and the Aux in the middle via the 3-wire, the black is hot and goes to the neutral on the Aux and gets passed to the right. The white is neutral and just gets bundled to pass to the right. The red is used for the single traveler between the Inovelli traveler terminal and the traveler on the Aux.