Development Completed :- 
Added a new field in existing NAV Send Order JSON payload named as 'multiBuyPromo' and capture the value from below Product's attribute from the Fluent JSON response file ("fluentFulfilments" --> MultiBuyPromo: True/False)  enable this for only non Customfit Item . Deployed in UAT.
Analysis and retrieval of Inventory Catalogue details from Fluent using a GraphQL query with Location Ref, Product Ref, and Inventory Catalogue Ref via Postman for standalone product inventory update.