Scope:

Unable to create a quote for any existing subscription for a upgrade in Salesforce ?

Error while trying to upgrade a subscription in Salesforce ?

List Index out of bounds error while  trying to upgrade a subscription in Salesforce ?

Summary: 

There is an issue when attempting to generate a quote for an existing customer using Salesforce in PC 1.0. The problem arises when navigating to the opportunity within Salesforce and attempting to create a quote for an existing subscription upgrade, resulting in an error.

Solution:

The issue stems from the presence of an addon in the subscription below. The problem lies in the inactive status of the pricebook entry for this addon. To resolve this, activate the pricebook entry for the addon, and the merchant should no longer encounter this error.