Welcome to Android Central! Which phone? Is Google+ updated to the latest version? Swipe in from the left--do you see your Google account listed there? Are you able to post using your computer browser?
It's an Android, using the Google+ app. I can see now that even my computer won't let me comment, saying "There was a problem updating your comment. Please try again."
That's the version of the operating system. I mean the phone's make and model. Like Samsung Galaxy S5, or LG G4. Go to Settings>About Phone>Model Name/Number to find out.
Yesterday I could post and comment but a few hours later I couldn't post or comment anything on my account I made a new account and I post and commented and it work so I don't understand why my other account won't let me post or comment anything I don't think I broke Google+ rule, so why can't I post or comment?