If you create sales transaction and the start date and end date is missing even after using the standard contract renewals form for sales transaction, you have to enable Sales Force Automation feature. This is a pre-requisite for SWV. If you try to add an item, you will get this error warning message:
"The Contract Item Start Date is earlier than the transaction Start Date.
Please enter a valid Contract Item Start Date."
To enable the feature, navigate to Setup > Company > Enable Features. Go to the CRM tab and check the box for Sales Force Automation feature then click Save.