In the CDR reporting, the Result column will show the appropriate error code should a call fail. You can get information about these error codes from this page -

SIP Response Codes

The negative result codes in the CDRs section can be interpreted using the following table:

Result Description
-1 External Translator Rejected the Call
-2 Body-less INVITE
-3 Account Expired
-4 Connection Capacity Exceeded
-5 Malformed SDP
-6 Unsupported Content-Type
-7 Unacceptable Codec
-8 Invalid CLD Translation Rule In Connection
-9 Invalid CLI Translation Rule in Connection
-10 Invalid CLD Translation Rule in Account
-11 Invalid CLI Translation Rule in Account
-12 Cannot Find the Session to Bind
-13 Invalid Translation Rule in DID
-14 No Rate Found in Tariff
-15 Call Loop Detected
-16 Too Many Sessions
-17 Account is in Use
-18 Calls per Second Exceeded
-19 Calls per Second on System Exceeded
-20 Insufficient Balance
-21 Destination is Forbidden
-22 No Rate Found in Tariff
-23 Routing Error
-24 Address is Incomplete
-25 No Routes Found
-26 Calls per Second Limit on Connection Exceeded
-27 Invalid Asserted ID Translation Rule
-28 CLD is in the Do Not Call List
-29 Invalid CLD Translation Rule in DID
-30 Call has been cancelled by calling party
-31 Call per Second Limit on Customer Exceeded
-32 Too Many Sessions for Customer
-33 Call Per Second Limit on Connection Exceeded
-34 Too Many Sessions for Connection
-37 CLI is in the Do Not Call List