I should have added that the HttpBuilder is adding a Content-Type: application/json header if no Content-Type is supplied, which is probably a bad behavior for a GET. I would still suggest pointing these at a Linux system with a listening netcat, though, so that you could see exactly how the HTTP requests were differing.

I was able to use that URL with a header of Content-Type: text/plain

And oddly no API key required, but that probably means there's some limiter. You may want to remove the image from your initial post, since you included your API key and where it goes.

Edit: I have made it such that in the next version no Content-Type header will be added to GET requests if missing.

I guess I have more questions about what you are trying to achieve -

Do you require the information retrieved from your external HTTP API to be available as data points / point values? (e.g. you want to store history for them in the Mango time series database, or you want the values to be available on the watch list etc) Is the external HTTP API available on the internet / accessible from the client web browser? If so you may be able to request the data directly from the web browser via a XHR request.