You attempted to initiate an outbound phone call, but the 'From' number you specified is not a verified number for your account. In order to use a phone number as the Caller ID on outgoing calls, you must first verify your ownership of that phone number.
You can verify phone numbers in the Console here.
If you received this error while trying to authenticate with your Test Credentials, you probably tried to make a test call with a From number from your live account. The only number that can be used to queue successful calls with your Test Credentials is +15005550006. For more information, read our documentation on the From number for making calls with your test credentials.
The From number used to make outbound call not a Twilio number or not a verified caller ID