3-way dimmer switch conundrum

I just one replaced a Leviton 3-way switch w a 3-way dimmer. Now, however, the light only goes in when both switches are "up". I experimented w swapping the 2 traveller wires at their terminals, and the light didn’t go on at all. I suspect this means I have the dimmer at the Load rather than Line switch. Is this true? Is there a fix? Is there a fix other than moving the dimmer to the other switch location? This is a 1916 house w old solid copper wiring, so the "code-ness" of things is a bit questionable. (There is, for example, no "green" ground wire in the box).

Addendum: I’ll have to reopen the box for photos (which was a pain to secure the wallplate) but note this is no Romex installation: these are all black cloth-covered solid copper wires, attached in a 4-gang to modern switches — two of which control, respectively, the 1st & 2nd floor chandeliers, also controlled by two switches in a 3-gang on the 2nd floor. I put the dimmer on the 1st-floor 3-way for the 1st-floor chandelier.

As to travellers: I installed the wires in the dimmer 3-way exactly as I removed them from the standard 3-way. I think that on testing, I was surprised that w new switch "off" the common was hot, but w switch "on" both travellers were hot … but that could be proximity probe not distinguishing bc wires are so close.