@Paul_Wintour the issue is just what @SeanP mentioned. You are using the version of the package that was built against the Dynamo 1.3 which didn’t use the new JSON based schema, and doesn’t have a proper constructors.
Now, I see that you went with that version because you want to use it with Revit 2018, but in this case I think its safe to use versions starting with 2019 (built against Revit 2019 API). Why? Because if there is a node in my package that uses any of the new APIs from Revit, it would simply not work, but rest of the package will work just fine, and they were all built against Dynamo 2.0 and higher so no duplicate ports there. You might get a warning that my package is looking for Revit 2019 dlls, but again, if Revit 2018 dlls are available, then it should all work, unless API specific to 2019 is used by a node.
So, please always use the LATEST package. Revit API version it was built against is a smaller concern than version of Dynamo you are on.
Cheers!