curl --request POST \
  --url https://api.example.com/EXPERIMENTAL_congestion_level \
  --header 'Content-Type: application/json' \
  --data '
{
  "method": "EXPERIMENTAL_congestion_level",
  "params": {
    "block_id": 1,
    "shard_id": 1
  },
  "id": "dontcare",
  "jsonrpc": "2.0"
}
'

{
  "result": {
    "congestion_level": 123
  },
  "id": "<string>",
  "jsonrpc": "<string>"
}