Android can't send text messages

[JA12]

I got a new Samsung Galaxy-A51 with Android 10, same account with 3. I can receive text messages but can't send any. It just comes back with "couldn't send message", I've checked the settings on the app and they all appear OK. Why is this happening?

[LauraH]

@JA12 Hi there, I'd like to help you out here. The first thing I'd like you to check is your message centre number, can you let me know what that's set to at the minute?

[JA12]

Which number? My phone number?

[billbond4]

Your SMSC number

[JA12]

After much hunting, the message center number is the same as my phone number, it's greyed out so can't be changed.

[JA12]

OK, after much hassle and downloading a different dialer, I managed to get at phone information and the SMSC. It was blank, so I tried update, got "update error", did reset, got "353879218648",145 still doesn't send text messages.