This issue is regarding dual sim iPhones.
If sending SMS message is attempted upon receiving an incoming call with the option to refuse call by using “Respond with Text” options on the incoming phone call screen, the SMS sending fails if an SMS has not been sent earlier to that caller from the receiving iPhone after a reset of its settings.
If sending SMS message is attempted upon receiving an incoming call with the option to refuse call by using “Respond with Text” options on the incoming phone call screen, the SMS sending fails if an SMS has not been sent earlier to that caller from the receiving iPhone after a reset of its settings.