When selling only a service item, Cin7 requires this to be a Service Sale rather than an order so then it can be authorised and the process completed which is different to a product Order. The CRM should support this in a way that when only a service item is added to a Quote and is confirmed, we should make a service sale in Cin7.
For our business we can sell just a service without any products. Cin7 Core to authorize a sale, it needs products in simple/advanced sale. If the order has a service only, it has to be pushed through as a "service sale" on Cin7 Core, which currently is not the case. We've had to make service as non inventory item for now, which means we still have to pick and pack and ship it, non inventory item can be sold without verifying their availability in stock. A service item does not require picking packing nor shipping usually.