If the check/money order payment option is enabled in the checkout, these ordered will need to be manually invoiced before the order is sent to the distributor via their API.
SALES > ORDERS
Select the desired order with a status of pending.
In the top right corner will be an option to invoice the order. Select invoice and on the next page select submit order.
This will send the order to the distributor and change the status of the order to processing because a payment was captured.
**Note: Order might not show up in your distributor account right away. Time frame depends on distributor.