Speckle Connector Tekla error

Hello Speckle Team, I’m Hesham and working as a BIM Coordinator in special steel structure projects which dealing with Tekla structure in which you manage, visualize the data, so I came across with Speckle and I found it so interesting after my first trail on Revit. but when it comes to the Tekla, the connector does not work, and the message error is " Null Reference Exception: Object reference not set to an instance of an object."

Can you please check the message and give me feedback?
thanks ahead.