My friend can no longer receive my text messages.

A few days ago, my friend stopped being able to receive my text messages. We have messaged each other for years. I can receive messages from him, but he can not receive them from me. Neither one of us has problems sending or receiving text messages from others.

I have an iPhone and he has an Android phone. We have not had any recent updates. We have not changed any settings on our phones. We have both restarted our phones.

I have looked through other community questions, but none seem exactly the same as my problem.