Can`t send or recieve picture text


The issue with my Galaxy S4 is that I can`t send or recieve picture text.
If I try to send one it says "invalid destination adress". I was thinking about checking the APN settings but I dont know how and where...
I`ve unlocked the developers options and I`m thinking about resetting it and maybe I`ll be able to use the phone after .. I don`t know what to do . Can anyone help ?