Mt.Everest Tile not found after converting

Hello, I am working on a Mapbox Three.js Helicopter Flight Simulator for Mt.Everest.

It would appear I need the terrain-rgb png tiles to create a texture height mesh. Unfortunately I am unable to get a tile from Mapbox's API. Can you determine if the issue is with this repo?

I was assuming I would enter the coordinates in Long, Lat (reversed) to generate X, Y coordinates and then pipe them into the v4/mapbox.terrain-rgb endpoint for raw png downloads.

https://api.mapbox.com/v4/mapbox.terrain-rgb/9/3209405.2294914094/9654494.533620872.pngraw?access_token=pk.eyJ1IjoibXBhY2Npb25lIiwiYSI6ImNrbjI5bXB1bDE1bDIydm1sZHl3NHRlM3QifQ.22OWoeAEOElNOu0W4ZsdFA

{ res: { message: 'Not Found' } }

Script

const queryMapbox = async () => {
  const merc = new SphericalMercator({
    size: 256,
  });
  const xyFromLatLong = (lat, long, merc) => {
    return merc.forward([long, lat]);
  };

  const zoom = 9;
  const long = 86.7278;
  const lat = 27.6857;
  const xyPos = xyFromLatLong(lat, long, merc);

  try {
    const response = await fetch(
      `https://api.mapbox.com/v4/mapbox.terrain-rgb/${zoom}/${xyPos[0]}/${xyPos[1]}.pngraw?access_token=${process.env.ACCESS_TOKEN}`
    );
    const res = await response.json();|
    
    console.log({ response });
    console.log({ res });
  } catch (err) {
    console.error(err);
  }
};

Start by reproducing the provided JavaScript queryMapbox script and inspecting the SphericalMercator forward conversion used to build the terrain-rgb URL. Compare the generated zoom, x, and y values with the Mapbox endpoint response; done means establishing whether the failure is caused by this repository or by the requested API coordinates or endpoint.