How to Handle Missing Product ID in Amazon Seller REST API?

I'm working with the Amazon Seller Central REST API, but I'mencountering an issue where I don't have a Product ID (such UPC, or FNSKU ,ETC) to identify the product.

Considering the GTIN exemption, should I first add the productmanually for specific product type and then proceed to post the new product using the API?

In case i want to add new product from rest api directly it always ask me to provide required filed merchant_suggested_asin or externally_assigned_product_identifier in other case which i dont want to i want to create my own listing