As a first step, please check this article: Importing Designs from Figma.
If the problem persists
We've seen this occasionally with Figma projects that are too big. When we try to pull in all of the slices, Figma's API returns an error.
Though understandably not ideal, one thing you could try on your end is to copy the assets you want to import into a brand new Figma file.
Assuming that file is smaller than the original, you should be able to sync with Animator after that.