3-Way Switch Not Working. Two Red Wires In Switch Box?

So I am trying to install a 3-way light switch with two Inovelli Blue switches, using this diagram:
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The auxiliary switch was easy enough to install, but I ran into an issue with the main switch. The switch box has two red wires. One red wire was connected to the switch, like shown in the diagram. The second red wire was connected to the two black wires (that go into the line of the Inovelli switch). I followed the wiring diagram as close as could, leaving the additional red wire not connected to anything:
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The Inovelli switch LEDs light up, but the light bulbs do not turn on. Where does the red wire go? Please advise, thanks!

Are you sure this is a 3-way (i.e. two switches)? When there are two 3-wires in a box, that suggests that this is the middle switch of a 4-way (i.e. three switches)(or more). There could be other reasons, but those aren’t typical.

Do you have pictures of the existing working switches before you tried to wire the Inovelli’s?

Please post pictures of both boxes with the wires pulled out fully. Need to see into the box as well, with the wires arranged so it’s clear to see all of the connections.

Also, go look for a 3rd switch. I know it sounds obvious, but there have been cases where someone discovered a 3rd switch they forgot about or didn’t know existed.

Hi Bry, thanks for helping!

I am sure that there are only two switches. I suppose there could be wiring for a third switch tied off in another box somewhere.

I don’t have a picture, but here is drawing of the initial wiring with the old switch:

The auxiliary box matches the earlier wiring diagram, with just the additional of a (unused) ground wire.