external_user_id is null when a workflow is triggered from an external app event

I have created a workflow with an HTTP webhook to mimic the asana-new-task event, so when a new task is created in Asana, the workflow is triggered and additional actions can be performed for that particular external user

I have created the trigger via pd.deployTrigger including the externalUserId. The trigger has been successfully created and I can see it in the list of triggers for that external user via https://api.pipedream.com/v1/connect/{my project}/deployed-triggers

Furthermore, when the user creates a task in Asana, the WF gets triggered and all parameters are passed as expected … but the external_user_id, which comes null in the event.context

Any ideas what I might be missing?