Declaration must be compatible: fix the PHP error

Before you start

Save the complete error line and its timestamp in a private note. Record the action that failed, the current PHP versionA PHP version is a numbered edition of PHP, like 8.3. Each edition is looked after for a limited time, then gets security fixes only, then nothing. and any components updated at the same time. Share only information needed for the investigation.

Public support forums are not suitable places for customer details, access credentials or complete server paths.

Back up both files and the database before making changes. Check that the backupA backup is a separate copy of your website's files and database, so you can bring the site back after a mistake, a hack or a failed update. is usable. Work on a restricted test copy with the same PHP version and relevant settings.

Disable real payments and outgoing customer emails there. Agree who will make the change and who will check the result. These steps are an investigation guide, not a diagnosis of your particular website.

Versions and responsibility

Ask your administrator to confirm the PHP version serving the affected website. Also record the WordPressWordPress is free software for building and editing a website in your browser. It is written in PHP, so it builds each page when someone visits., themeA WordPress theme is a ready-made package that decides how your WordPress site looks and how its pages are laid out. Change the theme and the design changes., plugin and bundled library versions involved. Establish which components changed during the same maintenance session.

A test using different code can give a different result even when its PHP version matches. Agree beforehand which user action will demonstrate a successful repair. Assign one responsible person to follow both the change and its acceptance check.

On the test copy, verify that scheduled jobs, payments and messages are actually separated from the live website.

Causes and PHP version

In PHPPHP is a programming language that builds your web pages on the computer that hosts your site, just before they reach the visitor. WordPress runs on it. 8, incompatible method signatures in inheritance cause a fatal error where some cases previously produced a warning. A signature describes parameters and the return type, among other things. Check whether an extension and its base library were updated together.

An updated plugin paired with older custom code is a useful investigation lead, not a diagnosis of your website.

Choosing the correct repair

Ask the developer to compare the overriding method with its parent contract. Review parameters, required values, visibility and return type. For third-party plugins, look for a maintained version combination first.

Removing type declarations without understanding the caller is not a repair. The method must still provide the result expected by every relevant calling path.

Five steps to a repair

1. Record both class and method names from the message. Match its timestamp to the failed page and save the installed component versions.
2. Identify the file containing the parent method and the file overriding it. Include custom extensions in a child theme in this investigation.
3. Compare the complete signatures against the installed library documentation. Have the maintainer update or adapt the incompatible extension on the test copy.
4. Run the affected action using ordinary input and a permitted empty input. Inspect the actual returned value as well as the visible page.
5. Open another page using the same class. Save the result and fresh logs before the administrator approves the tested change.

A practical check

A shipping module extending a base class provides a useful acceptance example. Calculate a test basket with a delivery address and one with incomplete address details. The first should show the expected shipping options; the second should follow the existing input validation.

Check the test order administration too. This is a proposed test, not a claim about a particular WooCommerceWooCommerce is a free add-on for WordPress that turns your website into a webshop, with products, a shopping cart and a checkout. plugin.

Getting help and checking the repair

Use the help form below if you cannot access the logs or do not know who maintains the affected code. Describe one failed action and the expected result. Ask for a proposal that separates the cause, the change and the acceptance check.

Do not include passwords with your request.

After the repair, repeat the original action on the test copy. Also check a normal visitor journey, an empty result and invalid input where relevant. Review fresh log entries at the new test time.

Keep versions and outcomes in your maintenance notes. Let the responsible administrator decide when the tested change can be applied to the live website.

Choosing the next step

Use the links below this article to choose the next step. The PHP update page helps you discuss maintenance with the administrator. Use the Exposure Check to check your PHP version.

Not every server exposes its version; confirm missing information with your host. This is a separate public check; do not treat its result as evidence that this programming error is repaired. Use the status page for current security information.

Keep the repair of the visitor action and the assessment of the server as separate checks in your notes. When requesting help, include the error text, the failed action and the expected result, but no passwords. Ask for one responsible person to oversee both the change and its acceptance.