I too have had this problem for a three months. Have tried everything. The reinstalled App still states it is ”…undergoing some last minute maintenance”.
Have been unable to gift data to my other accounts through App, which had previously been a seamless, easy task. Instead have needed to go through an hour long process of - accessing website, logging in, requesting call, waiting for response, confirming response, waiting for call link, using call link, going through verification, finally speaking to a very nice customer care person who then can organise my data gifting.
They are always very sorry to ‘hear of my difficulties’, but no explanation of why this is happening….
