php error

Code snippet was working fine with a snippet I put in several days ago. Today I went in to add a new snippet and upon submit the site blew up with Service Unavailable. Liquid Web staff got me back up. Because the problem was isolated to the code snippet plugin, I deleted the plugin and then reloaded the plugin. Upon reactivating the plugin the original problem of Service Unavailable occurred. Again Liquid Web staff got me back up and deleted the plugin.

I don’t know what to do. Reload a fresh download from WordPress Org and retry again or what? Need help.

Below is the error log:

PHP Fatal error:  Uncaught Error: Call to undefined function is_checkout() in /home/italianmarblefru/public_html/dev.italianmarblefruit.com/wp-content/plugins/code-snippets/php/snippet-ops.php(484) : eval()'d code:3
Stack trace:
#0 /home/italianmarblefru/public_html/dev.italianmarblefruit.com/wp-includes/class-wp-hook.php(307): kt_no_shipping_method_text('Error occurred ...', 'Error occurred ...', 'default')
#1 /home/italianmarblefru/public_html/dev.italianmarblefruit.com/wp-includes/plugin.php(191): WP_Hook->apply_filters('Error occurred ...', Array)
#2 /home/italianmarblefru/public_html/dev.italianmarblefruit.com/wp-includes/l10n.php(197): apply_filters('gettext', 'Error occurred ...', 'Error occurred ...', 'default')
#3 /home/italianmarblefru/public_html/dev.italianmarblefruit.com/wp-includes/l10n.php(297): translate('Error occurred ...', 'default')
#4 /home/italianmarblefru/public_html/dev.italianmarblefruit.com/wp-includes/class-wp-recovery-mode.php(177): __('Error occurred ...')
#5 /home/italianmarblefru/public_html/dev. in /home/italianmarblefru/public_html/dev.italianmarblefruit.com/wp-content/plugins/code-snippets/php/snippet-ops.php(484) : eval()'d code on line 3

I just want to reestablish the plugin on the site and add back the snippet that was working.

What do I need to do?