See explanation below. Explanation You need to edit the Lead to Opportunity Sales Process business process flow by making the step mandatory. In the site map, select Sales Settings. UnderCustomization, selectBusiness Process Flows. Select theLead to Opportunity Sales Processbusiness process flow. In theDevelopstage of the business process flow, select theCustomer Needstep. Tick theRequiredcheckbox to make this step mandatory. ClickSaveto save the changes. Reference: https://docs.microsoft.com/en-us/dynamics365/sales-professional/customize-business-process-flows