base = rate units of that currency. To convert from the base currency, multiply by the rate. To convert back, divide.
Rates are indicative market rates. They refresh about once a minute and don’t include fees. To price a specific payout or deposit with fees applied, and lock it, use POST /exchange-rate.
You can call this endpoint once per minute per account. Further calls in the same minute get
429 with a Retry-After header. Polling faster wouldn’t return newer data. To show rates against several bases, make one request and divide: the rate from A to B is rates[B] / rates[A].