Auto-invoice option can be configured at the service level. When this is enabled, invoices will be automatically sent for this service after a proposal is accepted. When it's disabled, invoices are not automatically created for this service, you have to manually invoice the services and send to your client
Manual invoicing steps are described here
You can manage auto-invoice option during the service creation or by editing an existing service after it's created
💡 If you update auto-invoice flag after it's created, this will be applicable only to the new proposals that will be created after that point, it won't apply to the existing proposals