I would recommend reaching out to your carrier to make sure text messaging isn't blocked from their side.
Also does this happen with all contacts or specific contacts?
What type of watch are you using?
Hi, for some time now I've not been able to send text messages using the Samsung galaxy watch 4g in standalone mode. I can make phonecalls in standalone mode without any issue. Samsung, please advise on this. Very frustrating when I go running without my phone.