On the Settings > General > Sales page, you can configure the mandatory fields in the sales form.

Check the Make the Client field required checkbox to prevent employees from creating a sale without entering client information.

Check the Make the Ad Campaign field required checkbox so that employees cannot create a sale without specifying the Ad campaign.

Reminder: you can set mandatory fields in the work order, lead, client, product, or asset forms in the Forms Editor.

Be sure to click Save to apply the selected settings.