You just bought your very own Personal User copy of Esri software from the Esri Store. You're excited that now you can use ArcGIS Pro. Now, all you need to do is authorize Pro so you can start using it.
You sign in to My Esri, and attempt to authorize Pro, but you get a warning message that you can't use your account to authorize Pro because your account is a public account.
This is because ArcGIS Pro uses the Named User license type, as explained in the ArcGIS Pro documentation.
Our colleague Kory Kramer has a lot of experience getting users up and running with ArcGIS Pro, and he has this advice: "If you sign in to arcgis.com and the page shows you as signed in but the URL still says www.arcgis.com/home/index.html, you’re using a public account and you won’t be able to use this to license Pro. You need to log in using the Named User account associated with your ArcGIS Pro license."
Read his full blog article here: How to Manage Your ArcGIS Pro License with ArcGIS Online