Items must be gridded, unless it's an individual item with no variance i.e. Wooden Baby Rattle. Because Shopify has built-in hot-swapping of items, they must be gridded for color, size, etc. Please follow this article for help on Gridding 

Note: You cannot have grids with the same name, if any grids have the same name you must update this before doing a push.

Images must be tied to the existing grid. Any images on the item level will not be synced, please ensure your images are attached to the grid level for all items. Follow this article on adding images to Grids. 

Descriptions need to be clean, Facebook will block all caps. A long description is not necessary but can be beneficial when you'd like to add additional information about your product. 

Sell on Shopify  - This field will need to be created as a "Pick From List" being either "Yes" or "No". This will allow you to easily filter the items that you want to push to Shopify. 

Tags - These are essentially keywords for product searches within Shopify's search engine. This is not required, but nice to have and highly recommended. Tags must be separated by ", " with a max character limit of 250 characters per tag. Example: "warm, cozy, sweater"

Product type -  This is the dropdown department in Shopify you want items to land in. Customers can use their pre-existing "Category" or "Department" field if they want it to be identical to their store, but most customers will have an additional organization within Shopify that they do not have in-store. If you will be using an existing field please make sure your options have been created as Product Types within Shopify.  If you don't map an item's custom field it will sync as a "Heartland Retail items" which is searchable, but not organically discoverable.