If you think that network is the culprit behind the problem of iPhone 13 or iPhone 13 Pro not sending texts messages, you can Reset Network Settings. Resetting network settings can be a pain because you lose wi-fi passwords and custom DNS, but it can also be a cure-all solution for many common networking issues with iPhone, including the inability to send messages. You can do this by going to Settings > General > Transfer or reset iPhone > Reset > Reset Network Settings. Enter your iPhone passcode and confirm. All you have to do is select the country, enter the phone number of the person you're attempting to get in contact with, and send your message. If you see a box to enter your email, this will allow the person you're sending a message to to respond to you via email. An email to SMS service allows you to send an email message to a corresponding email address, which is then converted into an SMS message and delivered to the recipient's mobile phone. This means that you can send a text to anyone with a mobile phone, regardless of whether or not you have a mobile phone yourself.