Go to Setup > Build > Develop > Custom Settings and click Manage for Config Custom Classes.
Click Edit beside Custom Classes.
For Cart Approval Callback Class, ensure the value is Apttus_CQApprov.CartApprovalCallback. This is required to have the Approval Required icon and Submit for Approval button in the Shopping Cart.
For Deal Optimizer Callback Class, ensure the value is Apttus_CPQOpti.DealMaximizerCallback. This is required to have the Approval Required icon and Submit for Approval button available when using Deal Maximizer.