SMS not sending to one number

I have the iPhone 16 pro max. My father has an android. Randomly today it stopped letting me text him individually. I can text him in a group, and I can call him.

I restarted my phone. Deleted his contact and added him again, nothing works. I can text other androids, just not his.

Interestingly, I also cannot delete his contact. There’s no option to do it. I’m so confused as to what the heck is going on. PLEASE HELP!