Are you sure you got the version that is for Canon? The 3rd party flash companies make different versions of the same flashes for use with Canon, Nikon, Sony, etc. The electronics and pin configuration in the shoe are different for each. In the case of Sigma, who also make cameras, there is even a Sigma version of most of their products.
Did you buy it new? Do you have the packaging? My Photttix flashes actually say "for Canon" on the front of the flash.
The comment above about making sure you seated it all the wAy forward into the hotshoe mount was also a good one. I have had that happen to me. Also, did you put good batteries into the flash? Did you get them in the right way? Typically they take 4 double A's. Also, 2 go in upside down, so you have to look carefully. Will it turn on and will it flash when you press "test"?
Scott
Canon 5d mk 4, Canon 6D, EF 70-200mm L f/2.8 IS mk2; EF 16-35 f/2.8 L mk. III; Sigma 35mm f/1.4 "Art" EF 100mm f/2.8L Macro; EF 85mm f/1.8; EF 1.4x extender mk. 3; EF 24-105 f/4 L; EF-S 17-55mm f/2.8 IS; 3x Phottix Mitros+ speedlites
Why do so many people say "FER-tographer"? Do they take "fertographs"?
