Shipping departments that are configured with an external fulfillment service will have a "LOG" button, clicking the log button will display the transmission activity with the fulfillment service.
The log page will differ depending upon the particular transmission mechanism / fulfillment integration, but the basic details will be "Filter" hyperlinks above the log entries for filtering the type of transmission log entries that appear:
There are three filter options (only two appear in the screenshot above):
You may need to inspect your log entries for troubleshooting transmission errors.
Clicking the "VIEW" button along the right side of a log entries will display the transmission details:
Inspecting the log details: