Skill repo will not sync to marketplace on claude.ai webinterface

On systems where I cannot install de desktop app or cli, I use the webinterface. The procedure to add the repo manually does not work:

Tried with these url formats:

• https://github.com/oracle/skills
• https://github.com/oracle/skills.git
• oracle/skills

Result is : Marketplace sync failed. Check the repository URL and try again.

To reproduce on Claude.ai web interface:

• go to settings
• plugins
• add marketplace --> add from repository