fetch and decode coinmarketcap JSON data with PHP using file_get_contents

Question

I want to display the current USDT Volume of upbit.

I have used coinmarketcap api for this. https://pro-api.coinmarketcap.com/v1/exchange/info

The problem i am facing is that it returns Undefined index: spot_volume_usd in.

What i am doing is

$url = "https://pro-api.coinmarketcap.com/v1/exchange/info?CMC_PRO_API_KEY={KEY}&slug=upbit"; 
$stats = json_decode(file_get_contents($url), true); 
$usdtvalue = $stats["spot_volume_usd"];


echo $usdtvalue."<br>";  

The api response is

{"status":{"timestamp":"2022-01-25T23:23:22.154Z","error_code":0,"error_message":null,"elapsed":9,"credit_count":1,"notice":null},"data":{"upbit":{"id":351,"name":"Upbit","slug":"upbit","description":null,"notice":"","logo":"https://s2.coinmarketcap.com/static/img/exchanges/64x64/351.png","countries":[],"fiats":["KRW"],"urls":{"twitter":["https://twitter.com/upbitglobal"],"chat":["https://pf.kakao.com/_DWxgVxl"],"website":["https://upbit.com/"],"fee":["https://upbit.com/service_center/guide"],"blog":[]},"tags":null,"type":"","date_launched":"2017-10-24T00:00:00.000Z","is_hidden":0,"is_redistributable":null,"maker_fee":0,"taker_fee":0,"spot_volume_usd":2684246187.212572,"spot_volume_last_updated":"2022-01-25T23:20:15.673Z","weekly_visits":3124629}}}

What is the best way to achieve this ? Thanks in advance!