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.