eBay Error: The quantity must be a valid number greater than 0.

When listing or delisting products to eBay you might encounter this error: 
The quantity must be a valid number greater than 0.

This error typically indicates that a setting in eBay must be changed in order for the stock of the product to update to 0.

To solve the error, check if the 'Out of Stock' feature is active on eBay for your eBay profile. To do this and to activate the feature: 

1. Navigate to your eBay Account Settings.

2. Under Selling, click on Selling Preferences.

3. Under Multi-quantity listings use the toggle to enable the option for 'Listings stay active when you're out of stock'.