If you are using custom preferences path in Houdini instead of the default one you see in the Envoy PLUGINS page, then download our HDAs and supporting files and extract them to the Houdini "otls" directory. The default location for this is:
Windows = C:\Users\%username%\Documents\houdiniXX.X\otls
Linux = ~/houdiniXX.X/otls
Mac = ~/Library/Preferences/houdini/XX.X/otls
In the same XX.X location add the attached gridmarkets.json file to the "packages" directory (creating the directory if it doesn't exist). Then (re)start Houdini.