Converter Help

[John Grocery]

Greetings,

I'm currently trying to use blockspring's XML to JSON converter to convert the XML format obtained from a databaseI(Supermarket API) to JSON before passing it to my web app. 

https://open.blockspring.com/pkpp1233/xml-json-explorer

I'm in the explorer page and currently trying to post the URL to the explorer and it gives me this.

my questions:

what does the API Error mean?

How can I use this explorer to convert the passed information from the input box(in bubble), to the URL to be converted with blockspring, and then passed back to bubble and displayed in the repeating group box.

Any help is greatly appreciated!!