Add site collection app catalog in the specified site.

• command: spo site appcatalog add -s|--siteUrl <siteUrl> --confirm
• siteUrl: absolute URL of the site where the site collection app catalog should be added
• confirm: suppress prompting for confirmation
• requires connection to a SharePoint site

For more information see the Add-SPOSiteCollectionAppCatalog cmdlet in the November release of the SPO PowerShell.