After upgraded, system related a invoice to "Service Contracts" rather than a Service ...
See online demo ...
Can you please explain?
Note that the online demo hasn't been updated in a long time
Sorry but I still don't understand. Please indicate more steps.
Click in line this invoice, system open a contract services ...
Try add another service in the same invoice
That link has always been for adding service contracts. That is the way it works.
But when I try to edit, system show products or services ...
How user add a contract services in invoice
the icons in the inventory lines will take you to assets (if it is a product) or to service contracts if it is a service. you click on the icon to add the asset/service contract