A known issue in the Pro 1.2 upgrade process may result in the following error being displayed when attempting to authorize single-use licenses:
"Unable to prepare your authorization."
This issue arises when using the ArcGIS Pro Software Update in earlier versions of Pro. The update fails to install the new version of the FlexNet licensing service needed by the Pro Software Authorization executable.
This error can also arise following a silent upgrade using the msi file.
<Pro install location>\ArcGIS\Pro\Resources\ArcGIS Pro Licensing Service\ProLS.msi