I don't understand what each ID means.

Please refer to the following ID definitions:

- sellerProductId (Listed Product ID)
This is an ID that you will see when a product is created completely. The ID cannot be changed.
Use this ID to bundle and manage products together.

- productId (Exposed Product ID)
Under a product sold on Coupang are the identifiers - 'item' and 'vendor item'.
This is an ID that can be changed anytime by merging, unmerging, etc.

- vendorItemId (Option ID)
This is the lowest-level identifier for products sold on Coupang. The ID cannot be changed. Because it is the lowest-level identifier, it is usually used as a key.

- sellerProductItemId
This ID can be obtained via Product Query API after a product is created completely. You need the ID to modify product option values.

- externalVendorSku (Seller Product Code)
This is a code of your choice that you can enter when you create a product and use for management. The input value is included when you look up the purchase order (PO).