does cast on ignite work on a mercenary ?

Im a mercenary and wanted to try out the cast on ignite skill. since im igniting a lot of enemies with my current setup.

after stacking enough INT through skill tree and gear i unlocked and equipped the skill thinking i can just put in skill gems and the selected skill would auto cast (Like totems for example)

but no matter what skill gem i try nothing seems to be able to slot into the gem.

am i missing something ? Why cant i just click on the Cast on Ignite empty skill slot and get a UI element with all the skills that CAN work on it ?

Cast on ignite reads:

While active, gains Energy when you Ignite enemies and triggers socketed spells on reaching maximum Energy.

Trigger SOCKETED SPELLS. If you are trying to put anything that isn't a spell, it won't work.

"

TheDutchman88#0359 wrote:

but no matter what skill gem i try nothing seems to be able to slot into the gem.

How about SPARK level 1?

hmm lessons learned i guess. perhaps ill look into applying marks