curl --request GET \
  --url https://api.prime.coinbase.com/v1/portfolios/{portfolio_id}/buying_power

{
  "buying_power": {
    "portfolio_id": "e8bbed13-fa33-41de-86d5-4335d8f08166",
    "base_currency": "BTC",
    "quote_currency": "USD",
    "base_buying_power": "3.8533347963443316",
    "quote_buying_power": "2051207.48454132"
  }
}