For example, if we are abroad with the OnePlus smartphone and want to avoid additional costs, a call barring function can be activated which blocks the corresponding outgoing or incoming calls.

The following options are available to us in the phone app

Note: When using Dual SIM, call barring can be set up individually for each SIM card.
The call barring password must be requested from the relevant network operator.

Android 10 (OxygenOS 10.0)
Step 1:  Open the  Phone app
Step 2:  Open the  menu
Step 3:  Open the  Settings
Step 4:  Tap on  Call accounts
Step 5:  Choose a  SIM card   (Dual SIM)
Step 6:  Tap on  Call barring
Step 7:  Choose an  option
Step 8:  Enter the  password  an tap  Turn on/off
  1. Open the Phone app
  2. Open the menu
  3. Open the Settings
  4. Tap on Call accounts
  5. Choose a SIM card (Dual SIM)
  6. Tap on Call barring
  7. Choose an option
  8. Enter the password an tap Turn on/off

OnePlus Instructions