Source Code - https://samelh.com/blog/2017/09/30/php-api-rate-limiting-redis/

api.php

<?php

use Predis\Client as PredisClient;

include __DIR__ . '/vendor/autoload.php';

function redis() {
    global $Redis;

    if ( !isset($Redis) || !$Redis instanceof PredisClient ) {
        $Redis = new PredisClient;
    }

    return $Redis;
}

function whatismyip() {
    if (isset($_SERVER['HTTP_CLIENT_IP']))
        $ipaddress = $_SERVER['HTTP_CLIENT_IP'];
    else if(isset($_SERVER['HTTP_X_FORWARDED_FOR']))
        $ipaddress = $_SERVER['HTTP_X_FORWARDED_FOR'];
    else if(isset($_SERVER['HTTP_X_FORWARDED']))
        $ipaddress = $_SERVER['HTTP_X_FORWARDED'];
    else if(isset($_SERVER['HTTP_FORWARDED_FOR']))
        $ipaddress = $_SERVER['HTTP_FORWARDED_FOR'];
    else if(isset($_SERVER['HTTP_FORWARDED']))
        $ipaddress = $_SERVER['HTTP_FORWARDED'];
    else if(isset($_SERVER['REMOTE_ADDR']))
        $ipaddress = $_SERVER['REMOTE_ADDR'];
    else
        $ipaddress = null;
    return $ipaddress;
}

function send_json($resp, $status=200) {
    header('Content-type: application/json; charset=utf-8');

    if ( $status ) { // status code
        http_response_code($status);
    }

    print json_encode($resp);
    die;
}

$limit = [
    'interval'      => 5, // seconds
    'num_requests'  => 2, // number of requests allowed per interval
    'user_ip'       => whatismyip(), // getting the user IP.
];

$uid = "requests_count_{$limit['user_ip']}";
$logged = (int) redis()->get($uid);

if ( !$logged ) {
    // first API request (or the count has expired)
    $logged = 1;
    // log the requests count to 1
    redis()->set($uid, $logged);
    // first time setting the key, expire the key at X seconds 
    redis()->expire($uid, $limit['interval']);
} else if ( $logged + 1 > $limit['num_requests'] ) {
    // send them a notice to slow down
    return send_json([
        'success' => false,
        'message' => 'Too many requests, please slow down or upgrade your API access plan.'
    ], 429);
} else {
    // get the time-to-live integer
    $ttl = redis()->ttl($uid);
    // set the key
    redis()->set($uid, $logged+1);
    // expire the key at X seconds (ttl)
    redis()->expire($uid, $ttl);
}

// Send the good response to the good users
send_json(['success' => true, 'data' => 'xyz']);