I use https://onlinetools.ups.com/api/rating/v1/shop

Returns several rates at the same time.

<?php

/**
 * Requires libcurl
 */

$curl = curl_init();

//Receive package info from query
$Weight = $_POST['Weight'];
$ReceiverZip = $_POST['Zip'];

//Set Receiver country
$ReceiverCountry = "US";

//Set your info
$UPSID = "YOUR UPS ACCOUNT NUMBER";
$ShipperName = "YOUR NAME";
$ShipperCity = "YOUR CITY";
$ShipperState = "YOUR STATE ABBREVIATION";
$ShipperZip = "YOUR ZIP";
$ShipperCountry = "US"; 
$clientId = "YOUR API CLIENT ID";
$clientSecret = "YOUR API CLIENT SECRET";

// Step 1: access token
curl_setopt_array($curl, [
  CURLOPT_HTTPHEADER => [
    "Content-Type: application/x-www-form-urlencoded",
    "x-merchant-id: ".$UPSID,
    "Authorization: Basic " . base64_encode("$clientId:$clientSecret")
  ],
  CURLOPT_POSTFIELDS => "grant_type=client_credentials",
  CURLOPT_PORT => "",
  CURLOPT_URL => "https://onlinetools.ups.com/security/v1/oauth/token",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_CUSTOMREQUEST => "POST",
]);

$response0 = curl_exec($curl);
$error = curl_error($curl);

curl_close($curl);

if ($error) {
  echo "cURL Error #:" . $error;
} else {
$tokenData = json_decode($response0);
$accessToken = $tokenData->access_token;
}

// Step 2: shipment data
$payload = array(
  "RateRequest" => array(
    "Request" => array(
      "TransactionReference" => array(
        "CustomerContext" => "CustomerContext"
      )
    ),
    "Shipment" => array(
      "Shipper" => array(
        "Name" => $ShipperName,
        "ShipperNumber" => $UPSID,
        "Address" => array(
          "AddressLine" => array(
            "ShipperAddressLine",
            "ShipperAddressLine",
            "ShipperAddressLine"
          ),
          "City" => $ShipperCity,
          "StateProvinceCode" => $ShipperState,
          "PostalCode" => $ShipperZip,
          "CountryCode" => $ShipperCountry
        )
      ),
      "ShipTo" => array(
        "Name" => "ShipToName",
        "Address" => array(
          "AddressLine" => array(
            "ShipToAddressLine",
            "ShipToAddressLine",
            "ShipToAddressLine"
          ),
          "PostalCode" => $ReceiverZip,
          "CountryCode" => $ReceiverCountry
        )
      ),
      "ShipFrom" => array(
        "Name" => "ShipFromName",
        "Address" => array(
          "AddressLine" => array(
            "ShipFromAddressLine",
            "ShipFromAddressLine",
            "ShipFromAddressLine"
          ),
          "City" => $ShipperCity,
          "StateProvinceCode" => $ShipperState,
          "PostalCode" => $ShipperZip,
          "CountryCode" => $ShipperCountry
        )
      ),
      "PaymentDetails" => array(
        "ShipmentCharge" => array(
          array(
            "Type" => "01",
            "BillShipper" => array(
              "AccountNumber" => $UPSID
            )
          )
        )
      ),
      "NumOfPieces" => "1",
      "Package" => array(
        "PackagingType" => array(
          "Code" => "02",
          "Description" => "Packaging"
        ),
        "PackageWeight" => array(
          "UnitOfMeasurement" => array(
            "Code" => "LBS",
            "Description" => "Pounds"
          ),
          "Weight" => $Weight
        )
      )
    )
  )
);

//Rate shop
curl_setopt_array($curl, [
  CURLOPT_HTTPHEADER => [
    "Authorization: Bearer " . $accessToken,
    "transId: string",
    "transactionSrc: testing"
  ],
  CURLOPT_POSTFIELDS => json_encode($payload),
  CURLOPT_PORT => "",
  CURLOPT_URL => "https://onlinetools.ups.com/api/rating/v1/shop",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_CUSTOMREQUEST => "POST",
]);

$response = curl_exec($curl);
$error = curl_error($curl);

curl_close($curl);

if ($error) {
  echo "cURL Error #:" . $error;
} else {
    $decodedResponse = json_decode($response, true); // true for associative array
    // Example using associative array
    if (isset($decodedResponse['RateResponse']['RatedShipment'])) {
        foreach ($decodedResponse['RateResponse']['RatedShipment'] as $shipment) {
            $serviceCode = $shipment['Service']['Code'];
            $rate = $shipment['TotalCharges']['MonetaryValue'];

            switch ($serviceCode) {
                case "01":
                    $ups_cost01 = $rate; 
                    break;
                case "02":
                    $ups_cost02 = $rate; 
                    break;
                case "03":
                    $ups_cost = $rate; 
                    break;
                case "12":
                    $ups_cost12 = $rate; 
                    break;
                default:    
                    break;
            }
        }
    }
}

?>