Cannot send texts to random people on S21

[NikitaNorman]

I've got a new S21, only had it a couple of weeks.

Randomly, it will not let me text people.  This may be right from the first try for a new exchange, or I could be in the middle of a conversation with them and then I can't text them any more.  I can't figure out why.  I've gone through the settings guide and everything is as it should be.

[Cleoriff]

@NikitaNormanSee if anything in this guide helps Guide: Text Message Tips (not sent or received) 

[NikitaNorman]

Nope, no good, unfortunately.  All settings are as they should be.  I tried the network trick and no joy.