The reason this error is happening is because you have set the "Input parameter entity" setting to: "MyFirstModule.Employee". The widget is expecting a single object as a top level object to use to retrieve your lower level location objects.
In your case you have set Employee for both "Input Parameter" and "Locations entity". The Microflow you are using has a parameter which is a LIST of Employee objects which does not match.
This is an example that would work with the case that you have Employees linked to a Branch:
You do not NEED to have an Entity like a Branch LINKED to your employees but, if you are using the Microflow option, the widget does expect a single parameter, that can be used to help you retrieve the Employee list
Hope this helps