By default, some of the standard fields in NetSuite are already set as Mandatory depending on the importance or impact of that field/s into the Transaction or Entity records. But if there are some other fields that user wants to set as Mandatory, here are the steps on how to do so.
NOTE: These steps apply on both Transaction forms and Entry forms.
1. Navigate to Customization > Forms > Transaction Forms or Entry forms > click Edit/Customize on the form where user wants to set the field/s as mandatory.
2. Click on the Screen Fields tab.
3. Click on the sub tab where the field is under.
4. Look for the field and check the box under the Mandatory column.
This is applicable for both standard and custom fields. To make custom field mandatory to all applied forms, see Settings Display Options for Custom Fields, Answer Id: 10097.
5. Click on Save.
To set these fields to non-mandatory, follow steps 1-3 and undo step 4 and click Save.