Once you go to Settings -> Channels -> eBay Main Options (or any other particular eBay instance in the account), you would be able to see the Large Merchant Services toggle, which by default is set to Off. Since it is a main setting for the instance and before enabling it, you can double check this guide, as it goes into further detail and you would be able to see more information about the way the solution is designed and please see the screenshot and details below:
eBay's Large Merchant Services make it possible for a Seller's application to send very large amounts of inventory to the eBay site, and to download single and multiple line item order information. These services have been designed to make a large merchant's workflow more efficient by leveraging eBay infrastructure to use parallel execution and to automatically retry on errors.
Advantages of Using Large Merchant Services:
- Shift the processing burden for large call volume (and call retries) from your servers to the eBay servers.
- Reduce your network bandwidth and connection requests significantly.
- Upload and manage price and quantity (near real-time) updates for thousands of eBay items.
- Manage your inventory by eBay Item ID or by SKU.
- Download large amounts of order, invoice, and active listing information.