Title: Undefined array key “HTTP_USER_AGENT”
Last modified: January 5, 2026

---

# Undefined array key “HTTP_USER_AGENT”

 *  Resolved [mailtobb](https://wordpress.org/support/users/mailtobb/)
 * (@mailtobb)
 * [4 months, 3 weeks ago](https://wordpress.org/support/topic/undefined-array-key-http_user_agent-8/)
 * Hi,
 * since a couple of days I get this error:
 * Warning: Undefined array key “HTTP_USER_AGENT” in /usr/www/xxx/live/wp-content/
   plugins/unipixel/woocomm-hook-handling/client-side-send-addtocart.php on line
   79
 * Any ideas how to solve it?
 * Thanks,
 * Bastian
 * The page I need help with: _[[log in](https://login.wordpress.org/?redirect_to=https%3A%2F%2Fwordpress.org%2Fsupport%2Ftopic%2Fundefined-array-key-http_user_agent-8%2F%3Foutput_format%3Dmd&locale=en_US)
   to see the link]_

Viewing 1 replies (of 1 total)

 *  Plugin Author [Buildio](https://wordpress.org/support/users/buildiodev/)
 * (@buildiodev)
 * [2 months, 2 weeks ago](https://wordpress.org/support/topic/undefined-array-key-http_user_agent-8/#post-18845962)
 * Hi Bastian,
 * Apologies for the delay in getting back to you.
 * This is a confirmed bug — on PHP 8.0+ the plugin assumes a User-Agent header 
   is always present, but some visitors (bots, crawlers, certain proxies) don’t 
   send one, which triggers the warning.
 * This will be patched in the next update! In the meantime the warning is cosmetic,
   it doesn’t affect tracking for real visitors, as browsers always send a User-
   Agent.
 * Thanks for reporting it.

Viewing 1 replies (of 1 total)

You must be [logged in](https://login.wordpress.org/?redirect_to=https%3A%2F%2Fwordpress.org%2Fsupport%2Ftopic%2Fundefined-array-key-http_user_agent-8%2F%3Foutput_format%3Dmd&locale=en_US)
to reply to this topic.

 * ![](https://ps.w.org/unipixel/assets/icon-256x256.gif?rev=3319375)
 * [UniPixel: Meta, Pinterest, TikTok, Google & Microsoft Server-Side Tracking for WooCommerce](https://wordpress.org/plugins/unipixel/)
 * [Frequently Asked Questions](https://wordpress.org/plugins/unipixel/#faq)
 * [Support Threads](https://wordpress.org/support/plugin/unipixel/)
 * [Active Topics](https://wordpress.org/support/plugin/unipixel/active/)
 * [Unresolved Topics](https://wordpress.org/support/plugin/unipixel/unresolved/)
 * [Reviews](https://wordpress.org/support/plugin/unipixel/reviews/)

 * 1 reply
 * 2 participants
 * Last reply from: [Buildio](https://wordpress.org/support/users/buildiodev/)
 * Last activity: [2 months, 2 weeks ago](https://wordpress.org/support/topic/undefined-array-key-http_user_agent-8/#post-18845962)
 * Status: resolved