MuJoCo

A plausible render proves little by itself. Follow the physical chain from model through kinematics, actuation, contact, and observation.

Start from the model

Read the MJCF and the pinned asset revision before adding control code. Check joint ranges, actuator limits, collision geometry, sites, masses, and the intended work surface.
Prefer a maintained model from MuJoCo Menagerie, but verify it against the real robot and task envelope.
Confirm gripper polarity, fingertip gap, and contact geometry empirically. Names and documentation can disagree with the model that actually runs.
Use the current MuJoCo documentation for MJCF and Python APIs rather than carrying signatures forward from memory.