executeUssd method
Executes a USSD code
ussdCode - The USSD code to execute
subscriptionId - (Optional) Subscription ID (SIM slot).
If not provided and there are multiple SIMs, the native selector will be shown.
If there is only one SIM, it is used by default.
Implementation
Future<UssdResponse> executeUssd(String ussdCode, {int? subscriptionId}) {
throw UnimplementedError('executeUssd() has not been implemented.');
}