After updating to WHMCS 8.11, you encounter an Oops error on pages containing a form protected by CAPTCHA:

Call to undefined method WHMCS\Utility\Captcha\LocalImage::getSiteKey()

This behavior is due to outdated customized template files.

If you have used template files to customize the appearance of WHMCS or used an after-market theme, you must update them for use with the latest version.

To resolve this specific error, apply this template update.

You can find all the template changes between each version of WHMCS in the Release Notes. For example, see the template changes between WHMCS 8.10 and WHMCS 8.11.

For more information, see Problems with one or more features following update.