on 15-11-2016 17:00
OnePlus 6 (O2 & Sfr), Z3 Tablet (Three UK), iPhone7 (EE)
on 31-12-2018 18:17
It looks like the chat is broken (for most browsers) because the security certificate for https://chat.o2.co.uk/ is no longer trusted by modern web browsers, as a result of the issuing authority's poor security practises. Internet Explorer 11 seems to work OK, as it's a very old browser, but using Firefox 64 I get the MOZILLA_PKIX_ERROR_ADDITIONAL_POLICY_CONSTRAINED_FAILED and a description stating the issuing authority is no longer trusted.