I encountered that kind of problem before. The message won't be sent and it wasn't RCS related problem but SMSC.
1. I shutted down the phone.
2. I removed the SIM cards.
3. I started the phone (without the SIM cards), that way it reset the SMSC number.
4. I then shutted down the phone again.
5. Inserted one SIM card and started the phone again, I tested it and it worked for that SIM.
6. I shutted down the phone again.
7. Inserted the second SIM card and started the phone.
8. Both worked that way.
If it helps, try also resetting the network settings but won't probably work.
*#*#4636#*#*
To check the SMSC number. SMSC number should be the same number as your SIM card number.
Google says.. "The SMSC (Short Message Service Center) number for Ethio Telecom is +251911299708 or +251911299709. If you are unable to send text messages, check your phone's SMS settings and set the service center number to one of these to ensure your messages are routed correctly."
Ask chat gpt for more explanation and steps.
Jan 23, 2026