Calls fail for a variety of reasons. SIP codes give us insights into reason for call failure.

503 code indicates that the server is unable to complete the call. This could happen due to multiple reasons. Whenever a call fails with 503 code, we recommend to check the call hang up code. If the call status is 'Failed 210', it indicates that the account does not have enough balance to complete the call.

We suggest to recharge the account and check. 

If the account has a positive balance and the call status code is other than 'Failed 210', contact our team via live chat or raise a ticket.