Take a look at this drawing to see if it makes sense. In essence, you are going to wire as a non-neutral. The Aux has to go in the box where power is first routed. The Aux gets that power (hot because it’s a non-neutral) and the white sends the hot to the dimmer box.
The red is used to connect the two travelers. The black in the dimmer box goes up to the light.
Double-check to confirm your wire colors match, or adjust accordingly.
