See Miva Merchant Shopping Cart Functions.
Note: The Order Manager does not automatically upload product changes to Miva Merchant. If you deal only with products (no attributes or options), you can upload a flat file of product data from the Order Manager for to Miva Merchant (go to Maintenance Menu>Import & Export tab>Export Inventory button). The recommended process is to make the changes in Miva Merchant and then download your product data to the Order Manager. Our import system allows you to 1) replace all data in the Order Manager, 2) replace fields like price & description or 3) only add new items. If you do use attributes and options, you must use this method to keep your product data in synch.