vAPI Plugin - "This method requires authentication" error

Hi

I have previously used the vAPI Plugin to do vCenter tags (properly against a vCenter 6.0) at one of my customers.

Now at another customer I am having issues with the vAPI Plugin and authentication.

I am running:
vRO 7.3.0.5481809 (Embedded in vRA 7.3)

vCenter Server 6.5.0.5973321

vAPI Plugin 7.4.0.5546687 (from here: Technical Preview version of VMware vRealize Orchestrator plug-in for vAPI))

I have added the vAPI Endpoint and vAPI Metamodel, and the objects are shown in the Inventory.
I can see all the scripting classes and methods related to vAPI in the API Explorer"List all tagging categories" I get the following error:

com.vmware.vapi.std.errors.unauthenticated => {data=<unset>, messages=[com.vmware.vapi.std.localizable_message => {args=[], default_message=This method requires authentication., id=vapi.method.authentication.required}]} (Workflow:List all tagging categories / Scriptable task (item1)#7)

If I duplicate the "List all tagging categories" workflow, and modify it, so that the line:

var client = endpoint.client();

Becomes:

var client = endpoint.client(myUsername, myPassowrd);

The workflow works.

So it seems as if the "session" created when adding the vAPI Endpoint / vAPI Metamodel, is not stored or at least not used.

Any way to get this to work properly, so I don't have to pass the username and password, to every workflow that needs to use the vAPI Plugin?