Hey Shan,
You actually return a specific value in your backend, which is rates.[currency]. So, you should return the whole object instead of one Item. Here is your code .then(json => json.rates[currency].toString());
it should look like this .then(json => return json;
then you can call each one just like json.date , json.base, json.rates .
Hope this helps you.
Best,
Mustafa