Can receive but not send text messages - "error 0"

[Adrianics]

Device is a Samsung S20e.

As the title says, I can receive but not send text messages; every time I try, it says "can't send message with O2 - error 0".

I've tried rebooting the phone and using a different SMS app.

Any ideas?

[Cleoriff]

@Adrianics 

See if this helps Guide: Text Message Tips (not sent or received) 

[Adrianics]

Thanks but unfortunately not, followed that guide beginning to end, checked everything, still not working

[MI5 · Accepted solution]

@Adrianics 

You need to contact O2.
All numbers are in this guide Guide: Coronavirus Community Help and Support 
When you call, you will be asked for the reason you are calling.
Stay silent for 15 seconds and you will be taken to the keypad options.
Press 2 for Everything Else
Press 5 for More Options
Press 7 for Anything Else which will put you though to someone.
You can also try saying "Upgrade" or "Fraud" to be connected to an advisor.
8.00am is the best time to call if you can.

[BarryM]

My issue was with a +44 UK mobile number (credit card company) who wanted a Y / N response. I found that by adding the number to my contacts (but using 07xxx) and then trying again, it worked 😉