If you still see "Samsung Messages chat registration failed," the problem is likely with your mobile carrier’s —specifically, their failure to support the Universal Profile 2.0+ standard. Contact their support and ask, "Does your IMS core support Google Jibe’s RCS for Samsung devices?" If they don't understand the question, it is time to switch carriers.
You need to accept a harsh truth: The Galaxy S25 series ships with Google Messages as the default. Samsung Messages still works, but RCS support is now a "legacy feature." samsung messages chat registration failed
If those didn't work, move to the real troubleshooting. If you still see "Samsung Messages chat registration