It is import the skeleton has the right pose when exporting variations for your Mixamo and Reallusion characters.
How Atoms reads those FBX files could vary from other host apps (i.e. Maya and Houdini).
This tool takes care of matching the skeleton pose within the host app to what Atoms is expecting. For this reason, users need to run this tool before exporting their variations.
The tool will first ask the user for the FBX containing the bind pose and then which software was used for creating such FBX.