How do I send a JSON POST request with cURL in PHP and handle errors?

Use curl_init with the right options, check both transport errors and HTTP status.

function apiPost(string $url, array $payload, string $token): array
{
    $ch = curl_init($url);
    curl_setopt_array($ch, [
        CURLOPT_POST           => true,
        CURLOPT_POSTFIELDS     => json_encode($payload, JSON_THROW_ON_ERROR),
        CURLOPT_RETURNTRANSFER => true,          // return body instead of printing it
        CURLOPT_HTTPHEADER     => [
            'Content-Type: application/json',
            'Accept: application/json',
            'Authorization: Bearer ' . $token,
        ],
        CURLOPT_CONNECTTIMEOUT => 5,
        CURLOPT_TIMEOUT        => 20,
        CURLOPT_FOLLOWLOCATION => false,
    ]);

    $body = curl_exec($ch);

    if ($body === false) {
        $err = curl_error($ch);
        curl_close($ch);
        throw new RuntimeException("cURL error: $err");
    }

    $status = curl_getinfo($ch, CURLINFO_RESPONSE_CODE);
    curl_close($ch);

    $data = json_decode($body, true, 512, JSON_THROW_ON_ERROR);

    if ($status >= 400) {
        throw new RuntimeException("API returned HTTP $status: " . ($data['message'] ?? $body));
    }
    return $data;
}

Why you got false or empty output

• Without CURLOPT_RETURNTRANSFER the response is printed and curl_exec returns true.
• TLS problems: "SSL certificate problem: unable to get local issuer certificate" means your PHP has no CA bundle. Set curl.cainfo in php.ini to a current cacert.pem. Do not disable verification (CURLOPT_SSL_VERIFYPEER => false) in production, it removes the protection of HTTPS.
• Sending an array to CURLOPT_POSTFIELDS posts multipart/form-data, not JSON. Encode it yourself.
• Missing Content-Type: application/json makes many APIs ignore the body.
• Redirects: a 301/302 from HTTP to HTTPS turns a POST into a GET if followed; use the final HTTPS URL.

Pitfalls

• Always set timeouts. The default is no timeout and a slow API hangs your PHP workers.
• Retry only idempotent requests, with exponential backoff.
• For production code, consider Guzzle or Symfony HttpClient (composer require guzzlehttp/guzzle), which wrap all of this.

Convert a command line request to PHP with the curl to code tool.