New eBay accounts (Business type) are typically restricted by certain eBay Seller Limits.
The limits are placed on the total number of SKUs you can list in one month and/or on the total merchandise. For example 50 SKUs and up to $500.
To compensate for those eBay Seller Limits we have a quantity rule in place. You can easily adjust the rule or disable it in Rules.
FYI: It is created by the system once you connect the eBay channel in Shoppingfeed and it'll be sending the quantity of 1 for all products that are in stock in your storefront. So, instead of listing a higher quantity of one and the same product, you can list a variety of products with a smaller quantity.
NOTE: eBay will review your account every month and adjust your limits automatically based on your sales volume and the feedback you receive.
You can also Request a seller limit increase in your eBay Seller account.