If you offer a set of primary services and a set of ancillary services, and only want your clients/agents to be able to select 1 primary service, this setting will allow you to do that.
First, navigate to Settings -- Office Settings -- Online Scheduler V3 Settings
Next enable this option.
Now, notice that once an order is being placed and a primary service has been added to the cart, other primary services are grayed out and you can only add ancillary services.
If you have any questions, please don't hesitate to open a chat or call our support team! (800)700-8112.