curl --request POST \
  --url 'https://rpc-mainnet.solanatracker.io/?api_key=' \
  --header 'Content-Type: application/json' \
  --data '
{
  "jsonrpc": "2.0",
  "id": 1,
  "method": "getTokenAccountBalance",
  "params": [
    "121k79rjdDy4QRuSykdG1Dw7pYCZSzKYrvs7RDKZTf1h"
  ]
}
'

import requests

url = "https://rpc-mainnet.solanatracker.io/?api_key="

payload = {
    "jsonrpc": "2.0",
    "id": 1,
    "method": "getTokenAccountBalance",
    "params": ["121k79rjdDy4QRuSykdG1Dw7pYCZSzKYrvs7RDKZTf1h"]
}
headers = {"Content-Type": "application/json"}

response = requests.post(url, json=payload, headers=headers)

print(response.text)

const options = {
  method: 'POST',
  headers: {'Content-Type': 'application/json'},
  body: JSON.stringify({
    jsonrpc: '2.0',
    id: 1,
    method: 'getTokenAccountBalance',
    params: ['121k79rjdDy4QRuSykdG1Dw7pYCZSzKYrvs7RDKZTf1h']
  })
};

fetch('https://rpc-mainnet.solanatracker.io/?api_key=', options)
  .then(res => res.json())
  .then(res => console.log(res))
  .catch(err => console.error(err));

<?php

$curl = curl_init();

curl_setopt_array($curl, [
  CURLOPT_URL => "https://rpc-mainnet.solanatracker.io/?api_key=",
  CURLOPT_RETURNTRANSFER => true,
  CURLOPT_ENCODING => "",
  CURLOPT_MAXREDIRS => 10,
  CURLOPT_TIMEOUT => 30,
  CURLOPT_HTTP_VERSION => CURL_HTTP_VERSION_1_1,
  CURLOPT_CUSTOMREQUEST => "POST",
  CURLOPT_POSTFIELDS => json_encode([
    'jsonrpc' => '2.0',
    'id' => 1,
    'method' => 'getTokenAccountBalance',
    'params' => [
        '121k79rjdDy4QRuSykdG1Dw7pYCZSzKYrvs7RDKZTf1h'
    ]
  ]),
  CURLOPT_HTTPHEADER => [
    "Content-Type: application/json"
  ],
]);

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

curl_close($curl);

if ($err) {
  echo "cURL Error #:" . $err;
} else {
  echo $response;
}

package main

import (
	"fmt"
	"strings"
	"net/http"
	"io"
)

func main() {

	url := "https://rpc-mainnet.solanatracker.io/?api_key="

	payload := strings.NewReader("{\n  \"jsonrpc\": \"2.0\",\n  \"id\": 1,\n  \"method\": \"getTokenAccountBalance\",\n  \"params\": [\n    \"121k79rjdDy4QRuSykdG1Dw7pYCZSzKYrvs7RDKZTf1h\"\n  ]\n}")

	req, _ := http.NewRequest("POST", url, payload)

	req.Header.Add("Content-Type", "application/json")

	res, _ := http.DefaultClient.Do(req)

	defer res.Body.Close()
	body, _ := io.ReadAll(res.Body)

	fmt.Println(string(body))

}

HttpResponse<String> response = Unirest.post("https://rpc-mainnet.solanatracker.io/?api_key=")
  .header("Content-Type", "application/json")
  .body("{\n  \"jsonrpc\": \"2.0\",\n  \"id\": 1,\n  \"method\": \"getTokenAccountBalance\",\n  \"params\": [\n    \"121k79rjdDy4QRuSykdG1Dw7pYCZSzKYrvs7RDKZTf1h\"\n  ]\n}")
  .asString();

require 'uri'
require 'net/http'

url = URI("https://rpc-mainnet.solanatracker.io/?api_key=")

http = Net::HTTP.new(url.host, url.port)
http.use_ssl = true

request = Net::HTTP::Post.new(url)
request["Content-Type"] = 'application/json'
request.body = "{\n  \"jsonrpc\": \"2.0\",\n  \"id\": 1,\n  \"method\": \"getTokenAccountBalance\",\n  \"params\": [\n    \"121k79rjdDy4QRuSykdG1Dw7pYCZSzKYrvs7RDKZTf1h\"\n  ]\n}"

response = http.request(request)
puts response.read_body

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "context": {
      "slot": 1114
    },
    "value": {
      "amount": "9864",
      "decimals": 2,
      "uiAmount": 98.64,
      "uiAmountString": "98.64"
    }
  }
}

{
  "jsonrpc": "2.0",
  "error": {
    "code": -32602,
    "message": "Invalid params"
  },
  "id": 1
}

{
  "jsonrpc": "2.0",
  "error": {
    "code": -32001,
    "message": "Unauthorized"
  },
  "id": 1
}

{
  "jsonrpc": "2.0",
  "error": {
    "code": -32005,
    "message": "Too many requests"
  },
  "id": 1
}

{
  "jsonrpc": "2.0",
  "error": {
    "code": -32603,
    "message": "Internal error"
  },
  "id": 1
}

{
  "jsonrpc": "2.0",
  "error": {
    "code": -32002,
    "message": "Service unavailable"
  },
  "id": 1
}

{
  "jsonrpc": "2.0",
  "error": {
    "code": -32003,
    "message": "Gateway timeout"
  },
  "id": 1
}