The Crypto.com provider is used to fetch the ticker price from the Crypto.com websocket API. The websocket is rate limited with a maximum of 100 requests per second. This provider does not require any API keys. To determine the acceptable set of base and quote currencies, you can reference the get instruments API.
To better distribute system load, a single market data websocket connection is limited to a maximum of 400 subscriptions. Once this limit is reached, further subscription requests will be rejected with the EXCEED_MAX_SUBSCRIPTIONS error code. A user should establish multiple connections if additional market data subscriptions are required. The names of the markets (BTCUSD-PERP vs. BTC_USD) represent the perpetual vs. spot markets.