Hii @purrlo
Have you completed running creation of line items API in which we send HS Product Id? Additionally this is the process to do the above:
1. Create Product in HS library using Create a Product . Save the object ID returned from HubSpot at your end.
2. Create a deal and save the deal id at your end
3. Run line items api using Create Line Item . The hs_product_id here is the object id from 1st step. Save the line item object id returned in 202 response.
4. Run Associate CRM objects to associate line items and deals. Use 20 as definition ID to associate line item to deal.
Thanks