Bug WHMCS-25204

[(Amr)]

I have reported the following on 19th Feb 2026 :

== Affected Version ==
WHMCS 9.0.1

== Description ==
When a client attempts to upgrade an existing yearly/recurring service to a one-time (lifetime) service, WHMCS throws a fatal DivisionByZeroError in includes/upgradefunctions.php inside SumUpPackageUpgradeOrder().
This happens on the latest WHMCS version running on PHP 8.3 and occurs even with all custom hooks/modules disabled, indicating a core issue.

This was working fine with PHP 7.4

ex :
Error: DivisionByZeroError: Division by zero in public_html/includes/upgradefunctions.php:0 Stack trace: #0 public_html/upgrade.php(0): SumUpPackageUpgradeOrder('9043', 10, 'monthly', '') #1 {main}

== Steps to Reproduce ==
Use the latest WHMCS version on PHP 8.3.
Create a recurring product (e.g., yearly billing cycle).
Create a second product with pay type “One Time”.
Set up an upgrade path from the yearly product to the one-time product.
Log in as a client with the yearly service.
Go to Client Area ? Upgrade/Downgrade and attempt to upgrade to the one-time product.
The upgrade page fails with a fatal error.

== Expected Result ==
The upgrade page should load normally

== PHP Version ==
8.3

== Severity ==
High 

This was confirmed to be a bug [ case WHMCS-25204 ].

Since then, two minor versions (WHMCS v9.0.2 & v9.0.3) were released, and this is not fixed yet!

[wtools]

It's unfortunate that they are still not fixed it

If you are affected, You should be able to handle this with a hook till they come up with a permanent solution.  

I had done some hook for upgrade handling in the past, so it should be possible. 

[(Amr)]

Unfortunately, the error happens before any hook is triggered, so no way to fix it on my end.

[(Amr)]

Any update on this ?

[Evolve Web Hosting]

2 hours ago, (Amr) said:

Any update on this ?

I have not tested this because I'm not using 9.x but this is an AI generated response that you could try on a test install by adding a hook and a small amount of code to clientareaproductdetails.tpl

<?php
/**
 * Fix: DivisionByZeroError when upgrading to a one-time product
 * Affected: WHMCS 9.x + PHP 8.x — upgradefunctions.php::SumUpPackageUpgradeOrder()
 *
 * Root cause: PHP 8.x throws a DivisionByZeroError where PHP 7.4 silently
 * returned 0. When upgrading to a one-time product, WHMCS attempts to
 * divide by the billing cycle days, which is 0 for one-time products.
 *
 * Save as: /includes/hooks/fix_upgrade_onetime_division.php
 */

// Hook files are loaded before upgrade.php runs its calculations,
// so we can register an exception handler here at file level to
// intercept the DivisionByZeroError before it becomes a fatal crash.
if (
    isset($_SERVER['SCRIPT_FILENAME']) &&
    basename($_SERVER['SCRIPT_FILENAME']) === 'upgrade.php'
) {
    // Capture any existing handler so we can chain it for unrelated errors
    $previousUpgradeExceptionHandler = set_exception_handler(null);

    set_exception_handler(function (\Throwable $e) use ($previousUpgradeExceptionHandler) {

        // Only intercept the specific bug — let everything else propagate normally
        if (
            $e instanceof \DivisionByZeroError &&
            strpos($e->getFile(), 'upgradefunctions.php') !== false
        ) {
            $serviceId = isset($_REQUEST['id']) ? (int) $_REQUEST['id'] : 0;
            header(
                'Location: clientarea.php?action=productdetails'
                . '&id=' . $serviceId
                . '&upgrade_error=onetime'
            );
            exit;
        }

        // Not our error — pass to the previous handler or PHP default
        if (is_callable($previousUpgradeExceptionHandler)) {
            call_user_func($previousUpgradeExceptionHandler, $e);
        } else {
            restore_exception_handler();
            throw $e;
        }
    });
}

/**
 * After the redirect, display a clear notice on the product details page
 * so the client knows what happened and what to do next.
 */
add_hook('ClientAreaPageProductDetails', 1, function ($vars) {
    if (empty($_GET['upgrade_error']) || $_GET['upgrade_error'] !== 'onetime') {
        return [];
    }

    return [
        'upgradeOnetimeError' => true,
        'upgradeOnetimeMessage' => 'Upgrading to a one-time payment product is not '
            . 'supported via the self-service upgrade tool. Please contact support '
            . 'and we will arrange this for you manually.',
    ];
});

 

Add to clientareaproductdetails.tpl

{if $upgradeOnetimeError}
    <div class="alert alert-warning">
        {$upgradeOnetimeMessage}
    </div>
{/if}