I am unable to see the delivery report of the failed API. Where can I find them?

There is a separate section for the Failed API. You can find it in the top menu of the delivery report section.

You can also find the Request ID, Date and Time on which the SMS was sent, Sender ID used, Mobile number to which SMS was sent, the message which was sent along with the reason why SMS was failed.

You can click on the code to see the reason of the failure or click here to see all the codes.