Generate a Brazilian invoice PDF in PHP

<?php
$payload = [
    'tipo'       => 'fatura',              // or 'recibo'
    'numero'     => '0001/2026',
    'data'       => '2026-08-07',
    'vencimento' => '2026-08-22',
    'emitente' => [
        'nome'      => 'Atlas Soluções Digitais LTDA',
        'documento' => '11.222.333/0001-81',   // check digits are verified
        'endereco'  => 'Av. Paulista, 1000 - São Paulo/SP',
    ],
    'destinatario' => [
        'nome'      => 'Comércio Silva & Filhos ME',
        'documento' => '22.333.444/0001-81',
    ],
    'itens' => [
        ['descricao' => 'Consultoria de implementação', 'quantidade' => 20, 'valor_unitario' => 250],
        ['descricao' => 'Licença mensal',               'quantidade' => 1,  'valor_unitario' => 349.90],
    ],
    'desconto'        => 100,
    'forma_pagamento' => 'PIX',
    'observacoes'     => 'Pagamento em até 10 dias.',
];

<?php
declare(strict_types=1);

const RAPIDAPI_HOST = 'brazilian-invoice-receipt-pdf-api-cpf-cnpj.p.rapidapi.com';

class InvoiceApiException extends RuntimeException
{
    public function __construct(public readonly int $status, public readonly string $code, string $message)
    {
        parent::__construct("[{$status}] {$code}: {$message}");
    }
}

/**
 * @return string raw PDF bytes
 * @throws InvoiceApiException
 */
function generateInvoice(array $payload, int $timeout = 15): string
{
    $json = json_encode($payload, JSON_UNESCAPED_UNICODE | JSON_UNESCAPED_SLASHES);
    if ($json === false) {
        throw new InvoiceApiException(0, 'encode_failed', json_last_error_msg());
    }

    $ch = curl_init('https://' . RAPIDAPI_HOST . '/invoice');
    curl_setopt_array($ch, [
        CURLOPT_POST           => true,
        CURLOPT_POSTFIELDS     => $json,
        CURLOPT_RETURNTRANSFER => true,   // return the body instead of echoing it
        CURLOPT_HTTPHEADER     => [
            'Content-Type: application/json',
            'X-RapidAPI-Key: ' . getenv('RAPIDAPI_KEY'),
            'X-RapidAPI-Host: ' . RAPIDAPI_HOST,
        ],
        CURLOPT_TIMEOUT        => $timeout,
        CURLOPT_CONNECTTIMEOUT => 5,
        CURLOPT_FAILONERROR    => false,  // keep the body on 4xx so we can read the message
    ]);

    $body   = curl_exec($ch);
    $status = curl_getinfo($ch, CURLINFO_HTTP_CODE);
    $curlErr = curl_error($ch);
    curl_close($ch);

    if ($body === false) {
        throw new InvoiceApiException(0, 'network_error', $curlErr);
    }
    if ($status !== 200) {
        $detail = json_decode($body, true) ?: [];
        throw new InvoiceApiException(
            $status,
            $detail['error'] ?? 'http_error',
            $detail['message'] ?? substr($body, 0, 300)
        );
    }

    return $body;   // binary-safe: PHP strings are byte arrays
}

$pdf = generateInvoice($payload);
file_put_contents(__DIR__ . '/fatura.pdf', $pdf);
echo 'wrote fatura.pdf (' . strlen($pdf) . " bytes)\n";

try {
    $pdf = generateInvoice($payload);
} catch (InvoiceApiException $e) {
    if ($e->code === 'invalid_params') {
        // One message, every problem, separated by "; "
        foreach (explode('; ', $e->getMessage()) as $problem) {
            error_log('invoice field error: ' . $problem);
        }
        http_response_code(422);
        exit(json_encode(['errors' => explode('; ', $e->getMessage())]));
    }
    if ($e->status === 429) {
        error_log('RapidAPI quota exhausted');
    }
    throw $e;
}

<?php
$pdf = generateInvoice($payload);

// Discard anything already buffered (a stray echo, a BOM, a warning).
while (ob_get_level() > 0) {
    ob_end_clean();
}

header('Content-Type: application/pdf');
header('Content-Disposition: inline; filename="fatura-0001-2026.pdf"');
header('Content-Length: ' . strlen($pdf));
header('Cache-Control: private, max-age=0, must-revalidate');
header('X-Content-Type-Options: nosniff');

echo $pdf;
exit;   // nothing after this - not even a closing PHP tag

# A healthy file starts with %PDF- at byte 0.
head -c 20 fatura.pdf | xxd | head -2
# 00000000: 2550 4446 2d31 2e37 ...   -> "%PDF-1.7"  OK
# 00000000: 0a25 5044 462d 312e ...   -> leading 0x0a = stray newline BEFORE the PDF

<?php
use GuzzleHttp\Client;
use GuzzleHttp\Exception\RequestException;
use GuzzleHttp\HandlerStack;
use GuzzleHttp\Middleware;
use Psr\Http\Message\RequestInterface;

function invoiceClient(): Client
{
    $stack = HandlerStack::create();

    // Retry transient failures only - never a 400.
    $stack->push(Middleware::retry(
        function (int $retries, RequestInterface $req, $response = null, $err = null): bool {
            if ($retries >= 3) return false;
            if ($err !== null) return true;                        // connection/timeout
            return in_array($response?->getStatusCode(), [500, 502, 503, 504], true);
        },
        fn (int $retries): int => 500 * (2 ** $retries)            // 500ms, 1s, 2s
    ));

    return new Client([
        'base_uri' => 'https://' . RAPIDAPI_HOST,
        'handler'  => $stack,
        'timeout'  => 15,
        'headers'  => [
            'X-RapidAPI-Key'  => getenv('RAPIDAPI_KEY'),
            'X-RapidAPI-Host' => RAPIDAPI_HOST,
        ],
        'http_errors' => false,   // same reasoning as CURLOPT_FAILONERROR
    ]);
}

function generateInvoiceGuzzle(array $payload): string
{
    $res = invoiceClient()->post('/invoice', ['json' => $payload]);
    $body = (string) $res->getBody();

    if ($res->getStatusCode() !== 200) {
        $detail = json_decode($body, true) ?: [];
        throw new InvoiceApiException(
            $res->getStatusCode(),
            $detail['error'] ?? 'http_error',
            $detail['message'] ?? substr($body, 0, 300)
        );
    }
    return $body;
}

<?php
function onlyDigits(?string $value): string
{
    return preg_replace('/\D/', '', (string) $value);
}

function checkDigit(array $nums, array $weights): int
{
    $sum = 0;
    foreach ($weights as $i => $w) {
        $sum += $nums[$i] * $w;
    }
    $rest = $sum % 11;
    return $rest < 2 ? 0 : 11 - $rest;      // NOT 11 - $rest when $rest is 0 or 1
}

function isValidCpf(?string $value): bool
{
    $d = onlyDigits($value);
    if (strlen($d) !== 11) return false;
    if (preg_match('/^(\d)\1{10}$/', $d)) return false;   // 111.111.111-11

    $n = array_map('intval', str_split($d));
    return checkDigit($n, range(10, 2)) === $n[9]
        && checkDigit($n, range(11, 2)) === $n[10];
}

function isValidCnpj(?string $value): bool
{
    $d = onlyDigits($value);
    if (strlen($d) !== 14) return false;
    if (preg_match('/^(\d)\1{13}$/', $d)) return false;

    $n  = array_map('intval', str_split($d));
    $w1 = [5, 4, 3, 2, 9, 8, 7, 6, 5, 4, 3, 2];
    $w2 = array_merge([6], $w1);
    return checkDigit($n, $w1) === $n[12] && checkDigit($n, $w2) === $n[13];
}

function isValidTaxId(?string $value): bool
{
    return strlen(onlyDigits($value)) === 11 ? isValidCpf($value) : isValidCnpj($value);
}