When exporting to Lottie, html works fine but the .json doesn't

The html file displays the animation correctly but I can’t get the json to work.

Here’s what LottieFiles shows when I preview the .json:

The number of frames is correct but it just shows that as a still image while it plays.

What I did:

  • List item Render a 3D animation in blender as a sequence of PNG files
  • List item Import the sequence into Synfig (File > Import Sequence)
  • List item Change the canvas size and number of frames
  • List item Saved the project
  • List item Plug-Ins > Export to Lottie format

Any ideas?