Agh, sorry your messages aren't going through, magenta5580990! According to our Text Message Troubleshooting: Message Blocking Active steps, if this is the only person you're trying to text and seeing this message in reply, then you'll want to have this friend check their own settings on their side! I know it's been a few days since your initial post -- have you had a chance to ask them? Or are you seeing this message when you text other folks as well?
I also have this problem with now two of my contacts. One of which is a family member on my plan! Neither of them have blocked my message. Please advice.