I don't do it that way - I just upload via the Web interface - Settings > Packages > New

Then just choose the file(package/DMG) you want to upload and the category > Save

I do use Jamf Administrator to sync back to an on site SMB distribution point

I tried the above you mentioned but the Error message " Package failed to upload" 

Please see the attached screenshot for more information.

Di it work ever?  If it did work before, do you have a firewall between you and Jamf Cloud?  If there is a firewall in place, have you seen the recent email about changes in IP addresses for Jamf Cloud?  Here's the current list that need to be allowed https://learn.jamf.com/en-US/bundle/technical-articles/page/Permitting_InboundOutbound_Traffic_with_Jamf_Cloud.html