In C4C message monitoring using Administrator -> Web Service Message Monitoring, you may see some inbound messages with a status of SPLIT.
What it means:
The SPLIT status for bulk messages occurs in C4C if at least one sub-message (or child) of a bulk message has an error during the posting time in C4C.
However if the bulk message is posted successfully (that means, all sub-messages are posted in C4C successfully), no split is going to happen for the message.
What to do next:
To see which child messages are getting the error, you can copy Message ID of the parent bulk message. Then do using the Advanced Filter (magnifying glass icon), put the message ID into the Parent ID field as a search.
You will see all the child messages and their statuses. In this way, you can view the invalid child messages, make the corrections as needed, and even Restart (or reprocess) the payload - hopefully to success.