Same as you: from the lu_invoke URL on my device, and the three links at the bottom of my previous post.
What does your baseURL look like? Note that my stateExtension URLs all start with & - if they didn’t then the binding might put in a / depending on how your baseURL ends. Per the documentation:
When concatenating the baseURL and stateExtension or commandExtension the binding checks if a proper URL part separator (/, & or ?) is present and adds a / if missing.
Note also that issues with properly loading Things files after they have saved are still a thing in OH3.
Either restart openHAB, or do this.