Hey mate, here is the screenshotPlease provide a screenshot of the developer console.
To open up the developer console if you're using chrome or whatever press F12 and then click 'Console', as well make sure you click 'Preserve Error Logs' to make the error logs stay on the console.
Still no luck and getting the same error in dev mode on chrome.The reason why it isn't working is because these links:
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Go to your external_variables.txt and scroll all the way to the bottom and check the url, make sure it doesn't have 3 dashes (/) and make sure it only has the one.