This is about licensing in ArcGIS Pro
I have installed ArcGIS Enterprise 10.9 on my server machine windows 2019.The ArcGIS Enterprise is licensed with ArcGIS Pro as it has GIS Professional user type. I installed ArcGIS license manager 2020.0 on the server. I launched ArcGIS License manager and checked authorize, version i checked Named User and used the JSON file for the portal to authorize ArcGIS Pro licenses. On my Desktop, windows 10 Pro I have installed ArcGIS Pro2.9. On licensing ,I configured licensing on ArcGIS Pro and pasted the web link for the portal. This prompted me to sign in and I received this error. Any help would be appreciated
My guess is that you will need to upgrade the license manager to a newer version to support 10.9+
I was using ArcGIS license manager 2021.1 and it didn't work
Agree with George on this one - you will need to upgrade using the workflow listed here - if that doesn't work, I'd recommend reaching out to Esri Support Services.
I am not an expert on this, but I think all of your versions (server, license manager, web adaptor, and desktop) all have to be the same version.