I can’t receive or send texts on my Samsung Galaxy J3 phone
Try using the Textra app:
Textra SMS - Android Apps on Google Play
If that doesn’t fix your problem there are some troubleshooting steps here:
and here:
For what it’s worth, the Android Messages on WiFi issue seems restricted to the S7, S7 edge and, perhaps, the S6. Android Messages is working on my J3.