// Created on savesnippets.com · https://savesnippets.com/BxyvlYNRpuRneu
<?php
function postJson(string $url, array $body, array $extraHeaders = [], int $timeout = 15): array {
    $ch = curl_init($url);
    curl_setopt_array($ch, [
        CURLOPT_POST           => true,
        CURLOPT_POSTFIELDS     => json_encode($body, JSON_THROW_ON_ERROR),
        CURLOPT_HTTPHEADER     => array_merge([
            'Content-Type: application/json',
            'Accept: application/json',
        ], $extraHeaders),
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_TIMEOUT        => $timeout,
    ]);
    $resp = curl_exec($ch);
    $code = curl_getinfo($ch, CURLINFO_RESPONSE_CODE);
    curl_close($ch);
    if ($code < 200 || $code >= 300) {
        throw new RuntimeException("POST failed: HTTP $code — $resp");
    }
    return json_decode($resp, true, 512, JSON_THROW_ON_ERROR);
}

$user = postJson('https://api.example.com/users', ['name' => 'Alice', 'email' => 'a@x.com']);