Add Usr Field from License Types to Licenses Form

Hoping someone can see what I’m doing wrong here.  I have added a Category field to the License Types Screen (FS200900) and am trying to get it to populate Read-only to the License Screen (FS201000).

I have tried this a number of ways but can’t get it to work.  Here is my latest attempt which gives me an error 

“Error: Cannot create the ctl00_phF_form_CstPXSelector1 control.
The PXSelector attribute is missing for the UsrLicenseCategory field.”

namespace PX.Objects.FS
{
  public class FSLicenseTypeExt : PXCacheExtension<PX.Objects.FS.FSLicenseType>
  {
    #region UsrLicenseCategory
    [PXDBString(10)]
    [PXUIField(DisplayName="Category")]
    [PXStringList(new string[] {"C", "V", "O"}, new string[] { "Credential Service","Vaccine", "Other"})]
    public virtual string UsrLicenseCategory { get; set; }
    public abstract class usrLicenseCategory : PX.Data.BQL.BqlString.Field<usrLicenseCategory> { }
    #endregion
  }
}


namespace PX.Objects.FS
{

  public class FSLicenseExt : PXCacheExtension<PX.Objects.FS.FSLicense>
  {
    #region UsrLicenseCategory
    [PXString]
    [PXUIField(DisplayName = "Category")]
    [PXDBScalar(typeof(
        Search<FSLicenseTypeExt.usrLicenseCategory,
        Where<FSLicenseType.licenseTypeID, Equal<FSLicense.licenseTypeID>>>))]
    public string UsrLicenseCategory { get; set; }
    public abstract class usrLicenseCategory : PX.Data.BQL.BqlString.Field<usrLicenseCategory> { }
    #endregion
  }
}

Thanks in advance!

Greg