Opportunity Product/Opportunity Line Item access in Salesforce

Opportunity Product/Opportunity Line Item in Salesforce represent Product2 products associated with an Opportunity.

The user must have the “Edit” permission on Opportunity records to create or update opportunity line items on an opportunity.

To add or edit opportunity products, below permissions are required
1. Edit on opportunities
2. Read on products and price books

Check whether Opportunity field FLS is given to the profile