How to enable MMS messaging on my iPhone 12 mini to send messages?

Hi stephie144! Thanks for reaching out to the Apple Support Community. No worries, we’ll get this sorted for you! 😊

First, let’s go to Settings > Messages and make sure MMS Messaging is turned ON. Also, ensure that Cellular Data is enabled, as MMS Messaging requires it and won’t work over Wi-Fi alone. Let me know if you need any more help! 

Do you mean "Messages," the included Apple messaging app? Or do you mean "Messenger," the Facebook/Meta app?