11-10-2023 19:45
11-10-2023 20:09
If it is just today, you may be being moved from the legacy to the new billing system, it will work again tomorrow. Try the web version first, https://accounts.o2.co.uk/signin to be sure it is not just your app playing up. All should be back after about 24hrs, otherwise contact O2, link below has all the ways, @Boh - good luck!
11-10-2023 21:33
Try deleting app, rebooting phone and then reinstall the app.