CSOM Iterate all SiteCollection in an SPO Tenant

I am trying to iterate over all site collections in a SharePoint Online Tenant.

I found this code on the web and adapted it to my needs:

        context = SharePointContextProvider.Current.GetSharePointContext(Context);
        ClientContext con = context.CreateUserClientContextForSPAppWeb();


        SPOSitePropertiesEnumerable spp = null;
        Microsoft.Online.SharePoint.TenantAdministration.Tenant tenant = new Tenant(con);
        int startIndex = 0;

        string sites = String.Empty;
        while (spp == null || spp.Count > 0)
        {
            spp = tenant.GetSiteProperties(startIndex, true);
            con.Load(spp);
            con.ExecuteQuery();


            foreach (SiteProperties sp in spp)
            {

            }
            startIndex++;
        }

But I keep getting the following error:

Current site is not a tenant administration site.

I am using the following library for accessing the tenants: C:\Program Files\SharePoint Client Components\Assemblies\Microsoft.Online.SharePoint.Client.Tenant.dll which has Version 15.

What am I doing wrong?