VTOL Drone Fliped While Takeoff Despite Correct Motor and Propeller Directions

I am building a Stallion VTOL from Flightory and have followed the official documentation for setup:
:page_facing_up: Stallion VTOL Manual

I have verified the following:
:white_check_mark: Motor and propeller directions match the documentation.
:white_check_mark: Radio inputs are mapped correctly.

However, the drone still crashes. Here’s a video of the crash:
:video_camera: Crash Video

Could this be a PID tuning issue, weight imbalance, or something else? Any insights would be highly appreciated!