Hi @jnlinn,
It is not very clear where you are adding the Cornerstone license. If you are already using the Pro and that is already validated, you don’t need to use the standalone Cornerstone. If you deactivate the Pro and use the standalone Cornerstone*, in that situation you need to validate and that is after adding the license into your Themeco Account. I have checked your Themeco Account, and found the Pro and the X license, not the Cornerstone standalone. Please add that before you validate.
NOTE: I have tried to check your website WordPress admin and found that the previously given credentials are not working.
Thanks