After a trading partner has accepted a proposal, you can finalize a quote/proposal by accepting the proposal, synchronizing products and prices with the related Opportunity and then create an Agreement.

After the quote/proposal has been presented to the trading partner either manually or via email, the Accept button is enabled. Selecting Accept signifies that the trading partner has accepted the Quote. If the current Quote is not primary, clicking the Accept button will make all other quotes non-primary and the current one primary.

Simultaneously, the line items in the Summary related list is synchronized back to Opportunity Products for forecasting purposes.

Alternatively, if the synchronization is not required to happen automatically, you can choose when to synchronize with the Opportunity by using the Make Primary and Synchronize with Opportunity buttons.

The Approval Stage must be in Presented stage.