I'm unable to backup my iPad due to iCloud storage issue

generally my IPad back-up automatically within few days of gap, but now I just don’t do the back-up even manually it just say “ this iPad cannot be backed up because there is not enough iCloud storage available “.

But the point is my iCloud have 3.8 GB of storage free if the check on website and even on my iPad.

[Edited by Moderator]