I have a polygon shapefile in CRS EPSG:27700 British National Grid that is a boundary of a study area that I would like to load into the iTree Canopy online tool. https://canopy.itreetools.org/index.php
The tool uses Google Satellite as its basemapping so in QGIS I have saved the layer with CRS EPSG:3857 WGS84
But when I try to load it I receive the error 'Invalid projection format'
The pop-up help tells me that the shapefile must be 'reprojected to geographic coordinates'
I have looked at the help video which essentially describes what I have tried to do above using QGIS - ie. reproject the shapefile into WGS84.
I also tried based on another web search using the Vector > Geometry Tools > Export/Add Geometry Columns
Is there something obvious that I am not doing?