What should I do or say back to him?

I sent this guy a message a couple days ago congratulating him on graduating. We dated last year and things got kind of messy between us. So, we haven't been on speaking terms, I also let him know that I wasn't mad at him anymore. Anyway, he responded back to me Thanking me for the congratulatons, and then he wished me to have a happy Independence day. Should I wait before I respond back to him? I am a little hesitant