Title: Fatal Error on PHP upgrade Last modified: July 7, 2026 --- # Fatal Error on PHP upgrade * [MarjoriesDaughter](https://wordpress.org/support/users/marjoriesdaughter/) * (@marjoriesdaughter) * [23 hours, 23 minutes ago](https://wordpress.org/support/topic/fatal-error-on-php-upgrade-2/) * I have inherited a site with a custom theme that was built around 2017. The site works fine in WordPress 7.0 running on PHP 7.4. But, converting to 8.x results in this error: Fatal error: Uncaught TypeError: call_user_func_array(): Argument# 1 ($callback) must be a valid callback, non-static method acf_edit_featured_image:: init() cannot be called statically … * Quite a few of the line numbers in the stack trace don’t make sense, but I undertand that this is normal. * I also understand from my research that WordPress 8.x is a lot finickier about having functions run with the init hook. So, I’m guessing that is the problem here. Should I start the search by searching for the function call_user_fun_arra() in the theme? * Thanks! You must be [logged in](https://login.wordpress.org/?redirect_to=https%3A%2F%2Fwordpress.org%2Fsupport%2Ftopic%2Ffatal-error-on-php-upgrade-2%2F%3Foutput_format%3Dmd&locale=en_US) to reply to this topic. * ![](https://ps.w.org/advanced-custom-fields/assets/icon.svg?rev=3207824) * [Advanced Custom Fields (ACF®)](https://wordpress.org/plugins/advanced-custom-fields/) * [Frequently Asked Questions](https://wordpress.org/plugins/advanced-custom-fields/#faq) * [Support Threads](https://wordpress.org/support/plugin/advanced-custom-fields/) * [Active Topics](https://wordpress.org/support/plugin/advanced-custom-fields/active/) * [Unresolved Topics](https://wordpress.org/support/plugin/advanced-custom-fields/unresolved/) * [Reviews](https://wordpress.org/support/plugin/advanced-custom-fields/reviews/) * 0 replies * 1 participant * Last reply from: [MarjoriesDaughter](https://wordpress.org/support/users/marjoriesdaughter/) * Last activity: [23 hours, 23 minutes ago](https://wordpress.org/support/topic/fatal-error-on-php-upgrade-2/) * Status: not resolved