original photos must be syncd to the cloud

Colinwiz,  TBMK you do not need to 'Send' original photos to portfolio.

When you are editing your Portfolio site you only need to click [Add] and select the [Lightroom Album] which will show the names (with one image) of the Lr-Classic synced Collections as they appear in Lr-Web.

I have not used Portfolio. The only reason I stated what I did is because the OP indicated that the original files had to be in the cloud. If that is the case then they cannot be added through Classic. If what you say is true then smart previews will work. That's all I know.

Lightroom Classic does not synchronize full-sized images to the cloud, but rather smart previews. In order to have the full-sized images in the cloud they must be added to Lightroom for the cloud using the Add option in that program.

File Sync Links that may help... all the links I have, since I don't know the cause of your specific problem
-FAQ https://community.adobe.com/t5/Get-Started/Helpful-Links-FAQ-Where-can-I-find-links-about-managing-and/td-p/7570118
-http://helpx.adobe.com/creative-cloud/help/sync-settings.html
-http://helpx.adobe.com/creative-cloud/kb/arent-my-files-syncing.html
-sync and email link https://community.adobe.com/t5/Get-Started/Email-link-of-file-in-personal-CC-folder/td-p/5944719
-an overview of assets https://assets.adobe.com/files
-File sharing https://community.adobe.com/t5/Get-Started/Does-Creative-Cloud-support-sharing-videos/td-p/7113392