message blocking is active? how do i turn that off?

[thunderlumber]

i received a reminder text regarding an upcoming appointment that asked me to reply "C" to confirm. when i reply, i get the message "free msg; unable to send message - message blocking is active". i had this occur on an old phone and found a way to turn this off, but for the life of me, and despite numerous google searches, im unable to figure out how on my current phone. its frustrating me to no end. any help would be appreciated. moto z2 play with android 8 OS. TIA

 

[BerryBubbles]

You might want to call & check with your carrier.

Several years back, I had that issue. Messages using Short Message Codes had been disabled. My carrier re-enabled the service.

It could be worth your time to check.