Undefined function after a PHP upgrade

Before you start

Save the complete error message and its timestamp in a private note. Record which page or action triggers it and what changed immediately beforehand. A screenshot of a blank page gives a developer less to work with than the first relevant log entry.

Do not post passwords, customer information or complete server paths in a public support thread.

Back up both files and the database before changing anything. Check how you would restore that 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. too. Prefer a restricted test copy using the same 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..

Disable real payments and outgoing customer emails on that copy. Change one thing per attempt and keep a note of it, so you can reverse an unsuccessful change without guessing what the previous setting was.

What is actually missing

A function is a named piece of code. It may belong to PHP, an additional server extension or your application. That gives the same message several possible causes.

An extension might be absent from the new PHP installation, or a file containing your application's function might not have been loaded.

The PHP 8.0 migration guide lists removed functions, including create_function(). Looking for a hostingWeb hosting is the service that keeps your website's files on a computer that is always online, so visitors can open your site at any time. switch to restore that function is the wrong repair: the application needs a compatible implementation. An extension function is a different case.

Ask whether its extension is available in the PHP environment that actually serves the website.

Five steps to a repair

1. Copy the exact function name, file and line from the first error. Record whether it happens during login, an import, a form submission or every page load. This narrows the investigation to the feature trying to call the function.
2. Check the active PHP version for the correct domainA domain name is the address people type to reach your website, such as yourcompany.com. It points visitors to wherever your site is hosted. using your hosting guide. For scheduled jobs, ask for the command line environment to be checked separately. The version shown in a terminal does not establish which version handles visitors.
3. Identify who provides the function with your developer. Is it custom code, a plugin or a PHP extensionA PHP extension adds functions to PHP that a website or application may need.? For a PHP function, check the official migration notes between the old and new versions. Keep the full name, including any namespace prefix.
4. Update the affected plugin or library on the test copy. If an extension is required, ask the host to enable it for the correct PHP version. If the function was removed, have the code replaced with a supported approach. Do not add an empty replacement function merely to hide the error.
5. Repeat the original action and compare the new log with your notes. Verify the result of the restored feature too. An import that no longer shows an error but creates no records has not passed its acceptance check.

A useful distinction

A message naming curl_init calls for a different investigation from a certificate error during a cURLcURL is a tool that lets software, such as PHP, fetch information from other websites and services, for example to check for updates or send an order. connection. In the first case, the function was unavailable when called. In the second, a connection was attempted.

Follow the related certificate guide only when the message actually concerns that connection.

When to get help

Use a developer when the function belongs to custom code, several plugins are involved or the affected integration processes payments. Follow the help button to the help form below and include the error text, version change and failing action. You do not need to include server access or a password in your initial message.

Check the result

Repeat the exact action that failed first. Then check login, a form submission and the main journey through your website. For a store, use a test order without a real charge.

Read the log for fresh messages with a recent timestamp. A working homepage alone does not establish that every affected function works again.

Keep the version numbers, the change and the outcome with your maintenance notes. Agree who will check the next update. Stop if the same error returns after the suspected cause has already been addressed.

Revisit the diagnosis instead of changing an increasing number of settings together. The aim is a repeatable repair that someone else can understand and verify.