The SMS center or also called "SMSC" ensures that an SMS finds its way from one mobile phone to another. Basically, it is a kind of router that determines the route of a sent SMS and then sends it on its way to the receiver.

Android 11/12/13
1. Open the phone app

2. Click on the icon if the app has not been launched before, otherwise perform step 3.3. Enter this combination

4. ,,Phone information"

5. Enter the SMS center (SMSC) of your network provider and save the entered phone number with "Update"