Some users can't login on iOS

SSO 2 factor authentication.
some users can’t log in, could you help to take a look? do you have encountered this issue?

Hi. It is impossible for anybody at Cloudflare to log into RingCentral App on an IOS device

no, our customer’s users most of them can log in, only more than 10 users can’t log in and encounter this attached file.

New login on IOS RingCentral app fails for anybody on cloudflare.com domain with this issue.