Set up custom invoice numbering

Add this code to site.php file:

Am_Di::getInstance()->hook->add(Am_Event::INVOICE_BEFORE_INSERT, function (Am_Event $event) {
    $di = Am_Di::getInstance();
    $period = date('Y_m');
    $counterKey = 'invoice_counter_' . $period;

    // Increment the counter atomically so concurrent checkouts get different numbers.
    $di->db->query(
        "INSERT INTO ?_store
            SET name=?, `value`=LAST_INSERT_ID(1), `expires`=NULL
         ON DUPLICATE KEY UPDATE
            `value`=LAST_INSERT_ID(CAST(`value` AS UNSIGNED) + 1),
            `expires`=NULL",
        $counterKey
    );
    $number = (int)$di->db->selectCell('SELECT LAST_INSERT_ID()');

    $invoice = $event->getInvoice();
    $invoice->public_id = sprintf('%s_%04d', $period, $number);

    $di->logger->debug(
        '[FIX:custom-invoice-number] Assigned invoice number {public_id}',
        ['public_id' => $invoice->public_id]
    );
});

This example produces numbers such as 2026_08_0001 and starts a new counter each month. You can change the prefix and formatting, but keep the complete value within the 64-character public_id limit. The database requires this value to be unique; if a duplicate is supplied, aMember replaces it with a randomly generated ID.

The counter is reserved before the invoice is saved, so failed invoice creation can leave gaps in the sequence.

For the widest payment-plugin compatibility, use only letters, numbers, and underscores. In particular, avoid dashes because some payment plugins use them to add or parse transaction suffixes.