{
    "inputs": {
        "variables": [
            {
                "name": "varURI-String",
                "type": "string",
                "value": "/_api/web/GetFolderByServerRelativeUrl('@{triggerBody()?['FolderPath']}')/ListItemAllFields/breakroleinheritance(copyRoleAssignments=false, clearSubscopes=true)"
            }
        ]
    }
}

Using a Power Automate Flow to break inheritance on a folder and this error was being returned. The issue turned out to be the path I was trying to use for the folder.

This did not work: LibraryName/Folder
This DID work: /sites/ParentSite/SubSite/LibraryName/Folder’