When Auto-sync is turned on, the system does validate for errors and auto-syncs the cart lines with the Proposal Lines. You can view the synced line items in the Quote/Proposal detail page under the Line Items related list. Auto-sync is done when the following conditions are satisfied:

• No error produced by the Validation callback
• No Constraint Rules error
• No line items in price pending state
• No Must Configure product is in configuration pending state