SF Symbols Outline stroke doesn't work, no validation

Hi Guys,
I am using custom icons which I want exported as SF symbols,
I am following the process of duplicating a current SF symbol and exporting a variable template,

on the variable template, I add my icons (Small, medium, and bold).
I had stroke icons so I adjust their thickness with stroke width and then proceed with “outline stroke”, however after I do this, my validation doesn’t work in SF Icons.
It gives me an interpolation error.

Any tips? I have also tried flattening icons.