I don’t know what exactly you’re trying to upload, but I know it’s not an SSL certificate we’ve provided.
That’s because you haven’t added the verification CNAME record yet, and so your SSL certificate hasn’t been issued yet.
Please add the CNAME record as specified on the certificate page in the client area, and wait for the SSL certificate to be issued. Then, upload the Private Key to the Private Key field and the Certificate to the Certificate field.