If the error says "Message Blocking is active" or a similar carrier message:
The phrase "message blocking" on an iPhone typically does not refer to a single iPhone setting. Instead, it is usually an error message from a cellular carrier indicating that a specific feature (e.g., sending SMS/MMS, premium messages, or international texts) is blocked on the user’s account. This report outlines the true causes and provides step-by-step solutions. how to turn off message blocking on iphone
If you aren't receiving messages from people not in your contacts: If the error says "Message Blocking is active"
If you accidentally blocked someone and want to receive their messages again: Open the app. how to turn off message blocking on iphone