Hi,
SXMB_MONI is the log for the pipeline steps executed in Integration Engine. As the message is processed successfully in IE and delivered to Adapter Engine, the message is showing successfully processed in SXMB_MONI. With respect to IE, there is no error.
When the message is received in Adapter Engine, it tries to send the data to Web service which is throwing error. So you can find the error in Message Monitoring -> Adapter Engine or in Communication Channel monitoring.
Suman