Hi Alexhig,
First, make sure that your Avatar includes Blendshapes. You can add the following parameters after the Avatar URL to get blendshapes: ?morphTargets=ARKit,Oculus Visemes, you can find more information from our Avatar API docs.
More on blend shapes can be found in our Forum Post here: [GUIDE] Blendshapes, morph targets and shape keys - #7 by vincent_x2o