How do I resolve this issue when trying to re-import a custom SF Symbol into Apple's SF Symbols app? Is there an exact export configuration I'm missing in Sketch or Figma?

I'm trying to make a custom SF Symbol. I've made some new custom symbols successfully, combining existing SF Symbols, so I understand the process. But as soon as I use vector files from my previous work, I get the error, "The provided variants are not interpolatable." - even though it has shapes made with vector path. Template set up - Variable I use sketch to work on the template I have separate layers for Ultralight-S, Regular-S, Black-S File saved as SVG What is wrong with my template? Thanks!