After breaking up, he said he could call him, but don't send him a message. What does that mean?

Maybe he has a new girlfriend or object. If you send him a message, it may be seen by his new object, which is not good. Cell phones are different. He can change your name into someone else's name when you can't get it, and then explain it to the new object. Although this kind of behavior is not a good behavior, it can indeed reduce the risk. But you scum had better not contact him.