@Patryk_F is partially correct. The NoTexting tutorial was written when the default ReceivingEnabled was Foreground. If you have this set to Off, set it to Foreground or Always. Following the discussion here to update the App Inventor 2 aia.
Problem Receiving SMS's - #2 by SteveJG to fix your aia.
The original App Inventor 2 version of the tutorial is circa 2014; it is now 2021 and changes to the AI2 compiler (additional components etc.)since the tutorial apk was built probably now result in a larger build. Don't worry about it.