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I am unable to text my son from my Apple Watch , he has a Samsung watch. I am able to text anyone else without any problems. Any ideas ?
Apple Watch Series 3, watchOS 6
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Did your son ever have an iPhone and use iMessage? He may need to deregister himself from iMessages
https://selfsolve.apple.com/deregister-imessage/
And on your end, SMS/MMS text messages, always require your iPhone's support, whether you have a GPS only or a Cellular Apple Watch. Where as iMessage and other Internet based messaging apps can use WiFi and Cellular LTE data without needing the iPhone.
https://support.apple.com/en-us/HT205547
Read the footnotes.