Transparency not fully transparent in pngs

Hi everyone, so I’m having a challenge with transparency. For context, I export png files of various body parts of a character - head, arms, torso, legs etc. They appear to be fine in isolation with a transparent background.

The issue is when I import them into my animation program - Toonboom Harmony Essentials. As the files are positioned on top of each other, you can see the ‘transparent’ area is not 100% transparent, making it obvious where the original frame edges are.

Before using Aseprite, I used a program called Hexels and had the same issue but the fix was - I would import it into the program PAINT.NET - select the transparent area with the magic wand tool, hit DELETE and re-save and viola!
For whatever reason, this same trick doesn’t work with the Aseprite exports.

Can anyone offer assistant how to resolve this, to export with a simple complete transparency?

An example is hopefully shown below:

Thankyou!