Please make sure the avatar body is built using the standard Roblox R15 rig type, with the correct joint placements, bone weighting, and part naming for each body segment (e.g. UpperTorso, RightUpperArm, etc.). The character should be fully compatible as an avatar bundle upload in Roblox Studio, without errors. Also, please ensure the avatar is scaled properly — not too short — and that deformation at joints (like knees and shoulders) bends naturally and smoothly during animation.
Face