If your iPhone is on WiFi calling/texting it doesn’t work sometimes. Try turning the WiFi off on the iphone for a few minutes and then try sending your texts. Afterwards, turn on WiFi, and the reset usually works after that. If not, turn off / on your iPhone.
You may also want to get Updates to Carrier towers, if you go to settings reset network should work. Here's how: Tap Settings > General > About. -- Carrier: If an update is available, you'll see an option to update your carrier settings.
You may also want to update the iPhone software, here's how: Settings > General > Software Update > Download and Install