You must include the sequence token obtained from the response of the previous call. An upload in a newly created log stream does not require a sequence token. You can also get the sequence token using DescribeLogStreams.
The batch of events must satisfy the following constraints:
The maximum batch size is 1,048,576 bytes, and this size is calculated as the sum of all event messages in UTF-8, plus 26 bytes for each log event.
None of the log events in the batch can be more than 2 hours in the future.
None of the log events in the batch can be older than 14 days or the retention period of the log group.
The log events in the batch must be in chronological ordered by their timestamp (the time the event occurred, expressed as the number of milliseconds since Jan 1, 1970 00:00:00 UTC).
The maximum number of log events in a batch is 10,000.
A batch of log events in a single request cannot span more than 24 hours. Otherwise, the operation fails.