I am not able to send or receive messages on iphone. I get "not delivered" then "try again" but no option to "send as text". Worked fine until two days ago. MMS and SMS are on.
Persistent Not delivered error usually is related to connectivity issues, so make sure you're connected to the internet, then double check your iCloud credentials by going to Settings and verify that you're logged in properly into your Apple ID account (you may also consider signing out and signing in again).