This article covers 

Access Denied: OP_UPSERT on chargebeeapps__CB_Subscription__c

SalesForce error

Solution 

The reason for the error is due to a permission issue. Now any profile other than Salesforce Admin, in addition to ChargebeeForSalesforceAdminUser also needs separate permissions on the below objects which include Subscription, Addon, and Coupon Line items.

Your user account might have lacked these permissions which caused the issue. We recommend you reach out to your salesforce Admin or ChargebeeForSalesforceAdminUser to view the permission sets for coupons and ensure that your account has the required access for coupons.

Once you update your access/ request the Admin user to re-run the sync and the issue will be fixed.