We both have iPhones but can't text each other?

My dh and I have iPhones and they are both updated. We can't send text messages back & forth. We can send a message to anyone else but not each other. How can we fix this? Some days this is the only way we can communicate while at work

Do you'll have iMessage set up to send & receive messages via your phone numbers?

Many automatically assume that that is the case since iMessage looks like it is a text app, but that is I'm (instant message, as in internet required). Check the settings for both phones & verify that.