Yes, I know that guide, I forwarded it already to 112nl :-). By the way, I have just received a reply. However, the response is clearly drafted using a script. I got the tips such as "please remove the first zero in the phone number", and "try it with and without wifi". It seems that the person is not technically skilled. I replied in a simple language that the problem is related with the attestation compatibility and insisted that the problem should be dealt with by developers of the app (in a very friendly way, of course). Now again waiting for the useful solution.