invalid access key for google apis

I would like to get the list of RSS feeds for YouTube channels to which I am subscribed.

I tried this way

$ curl 'https://www.googleapis.com/youtube/v3/subscriptions?key=BLA...BLA...BLA...'{"error": {"code": 400,"message": "API key not valid. Please pass a valid API key.","errors": [      {"message": "API key not valid. Please pass a valid API key.","domain": "global","reason": "badRequest"      }    ],"status": "INVALID_ARGUMENT","details": [      {"@type": "type.googleapis.com/google.rpc.ErrorInfo","reason": "API_KEY_INVALID","domain": "googleapis.com","metadata": {"service": "youtube.googleapis.com"        }      }    ]  }}

As you can see there is some problem

API key not valid. Please pass a valid API key.

Also if I connect to https://console.cloud.google.com/apis/credentials?hl=it&project=yt-rss-342415&supportedpurview=project&pli=1I see that the key is valid.

So what's the problem?

EDIT

Sorry, the API_KEYit was incorrect.
I fixed!
But it still doesn't work

# SYNTHESIS{"error": {"code": 403,"message": "Requests from referer \u003cempty\u003e are blocked.","errors": [               {"message": "Requests from referer \u003cempty\u003e are blocked.","domain": "global","reason": "forbidden"            }        ],"status": "PERMISSION_DENIED","details": [            {"@type": "type.googleapis.com/google.rpc.ErrorInfo","reason": "API_KEY_HTTP_REFERRER_BLOCKED","domain": "googleapis.com",  –

Why?