I have the same problem. Every other function I've used works fine, but update_role fails with the same "'user' parameter required or invalid" error. I am using a slightly older arcgis Python library, 1.5.1, but that is what my company is using with its official ArcGIS Pro install so I'm pretty much stuck with it for now. I'm using the Python api to work with my company's ArcGIS Online domain: <domain>.maps.arcgis.com
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