How to have the counter of characters when I am writing a texto (SMS)? I have my new iPhone 6S, on iOS 9.

I would like to have the counter of characters when I am writing a texto (SMS). How can I have that?

I have turned on the setting for that. But for some recipients that does not work.

Thank you.
Character count setting in iPhone Settings is only for SMS messages.  It doesn't work for apps from other developers.  You would need to contact the developer of Texto to determine how to do character counts.