Title: Bug: is_checkout() function error Last modified: September 9, 2026 --- # Bug: is_checkout() function error * Resolved [Pieter Sand](https://wordpress.org/support/users/beachholiday/) * (@beachholiday) * [1 day, 23 hours ago](https://wordpress.org/support/topic/bug-is_checkout-function-error/) * Dear Support, We are experiencing an intermittent issue on our website. * On September 9, 2026, the /feed/ URL returned a 500 error with the following message: Call to undefined function PaymentPlugins\Stripe\is_checkout() * My hosting provider confirmed that the is_checkout() function exists in WooCommerce 11.1.0, but it was not available during the affected request. They also found several other WooCommerce file-loading errors in the server logs around the same period, including an instance where a required WooCommerce file could not be loaded. * Could you please investigate whether this is an issue that can be addressed on your end, or advise if there is anything I should check on my side to help prevent it from happening again? * The error appears to occur intermittently and is not present on every request, based on the server logs. WooCommerce: 11.1.0WooCommerce Stripe Payment: 4.0.13 * Many thanks for your help with this. * Piet Viewing 4 replies - 1 through 4 (of 4 total) * Plugin Support [Gabriel – a11n.](https://wordpress.org/support/users/gabrielfuentes/) * (@gabrielfuentes) * [22 hours, 40 minutes ago](https://wordpress.org/support/topic/bug-is_checkout-function-error/#post-19017076) * Hi Piet! * Since this is a Stripe for WooCommerce issue, would you mind opening a new thread on the Stripe Payments forum? I’m adding the link below so my colleagues can help you further: * [https://wordpress.org/support/plugin/woocommerce-gateway-stripe/](https://wordpress.org/support/plugin/woocommerce-gateway-stripe/) * I’ll be closing this one, as it’s exclusively for WooCommerce Core issues. * Thank you! * Thread Starter [Pieter Sand](https://wordpress.org/support/users/beachholiday/) * (@beachholiday) * [11 hours, 32 minutes ago](https://wordpress.org/support/topic/bug-is_checkout-function-error/#post-19017485) * Dear Gabriel ( [@gabrielfuentes](https://wordpress.org/support/users/gabrielfuentes/)) * Many thanks for your reply. * This is the plugin we use for Stripe payments: [https://wordpress.org/plugins/woo-stripe-payment/](https://wordpress.org/plugins/woo-stripe-payment/) * I contacted the developer of this plugin and he advised that he believes it is a core WooCommerce bug rather than specific to Stripe. * However, I posted the same in the forum you suggested. * Many thanks for your help. * Piet * Plugin Support [Gabriel – a11n.](https://wordpress.org/support/users/gabrielfuentes/) * (@gabrielfuentes) * [8 hours, 44 minutes ago](https://wordpress.org/support/topic/bug-is_checkout-function-error/#post-19017664) * Hi Piet! * Thanks for confirming which plugin you’re using. I assumed it was the official WooCommerce Stripe one, which is why I pointed you there, so sorry about the mix-up. * I don’t think the answer you got from that plugin’s support team is right though. Looking at the log you shared: * `On September 9, 2026, the /feed/ URL returned a 500 error with the following message: Call to undefined function PaymentPlugins\Stripe\is_checkout()` * That error comes straight from their plugin (you can see its name there), not from WooCommerce core. An easy way to confirm: deactivate their plugin and leave only WooCommerce core active, and the error goes away. * Their plugin is an extension that adds Stripe features on top of WooCommerce’s core functionality, so it depends on the core to work. If it isn’t compatible with the current version of core, that’s something their developers need to fix on their end. Otherwise every user of that plugin would hit the same error and wouldn’t be able to use it. * I’d go back to them with that and, if you can, ask for a different support rep. * If they still send you back to us (which they shouldn’t), it might be worth looking at a different Stripe plugin instead 🙂 * Cheers * [Clayton R](https://wordpress.org/support/users/mrclayton/) * (@mrclayton) * [5 hours, 35 minutes ago](https://wordpress.org/support/topic/bug-is_checkout-function-error/#post-19017832) * Hi [@gabrielfuentes](https://wordpress.org/support/users/gabrielfuentes/) * I believe this thread needs some clarification since you’re recommending [@beachholiday](https://wordpress.org/support/users/beachholiday/) use a different Stripe plugin. * The communication to [@beachholiday](https://wordpress.org/support/users/beachholiday/) was the following: * ```wp-block-code This looks like an issue on the server where the WooCommerce files were not loaded at some point during a request. ``` * The Payment Plugins team did not communicate that this was a WooCommerce core issue. It’s possible the user’s site has an optimization plugin installed that selectively excludes plugins loading on certain requests where the plugin is deemed to not be needed. * Thanks Viewing 4 replies - 1 through 4 (of 4 total) You must be [logged in](https://login.wordpress.org/?redirect_to=https%3A%2F%2Fwordpress.org%2Fsupport%2Ftopic%2Fbug-is_checkout-function-error%2F%3Foutput_format%3Dmd&locale=en_US) to reply to this topic. * ![](https://ps.w.org/woocommerce/assets/icon.svg?rev=3640790) * [WooCommerce](https://wordpress.org/plugins/woocommerce/) * [Frequently Asked Questions](https://wordpress.org/plugins/woocommerce/#faq) * [Support Threads](https://wordpress.org/support/plugin/woocommerce/) * [Active Topics](https://wordpress.org/support/plugin/woocommerce/active/) * [Unresolved Topics](https://wordpress.org/support/plugin/woocommerce/unresolved/) * [Reviews](https://wordpress.org/support/plugin/woocommerce/reviews/) * 5 replies * 3 participants * Last reply from: [Clayton R](https://wordpress.org/support/users/mrclayton/) * Last activity: [5 hours, 35 minutes ago](https://wordpress.org/support/topic/bug-is_checkout-function-error/#post-19017832) * Status: resolved