How do I fix iMessage sending SMS only to my wife's iPhone?

Hey everyone. My wife and I have been texting with no issues with iMessage since we both got our new phones. Both of us have 18 ProMax. Yesterday afternoon my phone starting sending SMS to her only. iMessage to my sister, my son, family, friends, it just stopped to my wife’s phone. I have gone in the settings and toggled iMessage on/off, checked for my phone number, reset the phone, made sure I’m on cellular or WiFi, done everything google suggests and cannot for the life of me get it to work. Anyone else had this problem and how did you fix it? Thanks in advance.

[Re-Titled by Moderator]

Original Title: iMessage Problem