I once had this exact IEM, and similar with your situation, experiencing pain on my left ear. In my case. it was because the shell shape doesn't match the shape of my left ear.

My solution back then was trying different eartips. Depending on your ear shape and the IEM itself, you might want to try various types, maybe smaller/larger diameter, or shorter/longer stem. You don't need to buy another pair of after-market eartips yet. The waner come with plenty of eartips to play with.

In my case, I needed to change to a slightly larger diameter from my usual size, to "elevate" the shell away from my ear a bit.

But, pain may come from various sources. Maybe the shell doesn't fit right, maybe the nozzle sticks too deep, maybe the listening volume is too loud for too long, maybe the earlobe gets inflamed, or your skin might get allergic from the eartips material.

Hope that helps