It is impossible to tell with this much information. It suggests that there is an issue connecting to the Twilio API.
Is internet access enabled in your manifest?
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.app"> <uses-permission android:name="android.permission.INTERNET" />
If the application running in an emulator or on a physical device.
If emulator, check the emulator can access the internet? (It may be on airplane mode by default)
Check you can access https://api.twilio.com in a standard browser.

if you're using vscode you would get gai_error=0 that's if the http is connected successfully
Here is the right place to place the internet permission because it was quite challenging to know the location
<manifest xmlns:android="http://schemas.android.com/apk/res/android" package="com.example.appName"> <uses-permission android:name="android.permission.INTERNET" />
run the flutter run command on cmd or visual studio code terminal