In case of low (zero) account balance in Twilio,
1. Will Twilio stop to hit the Application VoiceUrl associated with the account
2. Is there any way to know the low balance without reaching Twilio console?
Twilio developer evangelist here.
When you are at a low, non-zero balance, Twilio will continue to act as normal.
When you hit zero, from the Twilio help centre:
When your account balance reaches zero you will no longer be able to make and receive phone calls or send and receive SMS messages. You won't lose your phone numbers right away.
We will continue to bill your account for 60 days for the phone numbers you've purchased. If you pay off your balance and fund your account with a minimum of $20, you’ll be able to use your phone numbers again. After 60 days, if you haven't replenished your Twilio account balance, we may close your account and return your phone numbers to our pool of available numbers.
In order to stop your account seizing up, you can set up an auto recharge trigger which will top up your account when it gets low.
Alternatively, according to this page
It is possible to also set a notification trigger that will just email you when your balance falls below a chosen threshold. If you'd like to enable this please contact Support.
So, you can get a trigger at a chosen balance which you know.
Let me know if this helps at all.