Generate hc-transform using QGIS

After re-projection of your map layers, then to know about CRS transformation follow the steps

Step 1: Open Projection Properties Dialog:

Use Ctrl+Shift+P in windows or Cmd+Shift+P on Mac to open Projection properties dialog.

Step 1: Add HC-TRANSFORM in your GeoJSON file:

Now add following hc-transform in your GeoJSON file like in the below image.

"hc-transform":{ 
    "default":{
        "crs":"+proj=mill +lat_0=0 +lon_0=0 +x_0=0 +y_0=0 +R_A +datum=WGS84 +units=m +no_defs"
    }
}