As reported on the Zen Cart support-thread, the following debug-log results:
[18-Jan-2022 09:44:24 ] Request URI: /index.php?main_page=pricelist&profile=1, IP address: ::1
#1 require(...\includes\templates\template_default\pricelist\tpl_main_page.php)
called at [...\index.php:94]
--> PHP Warning: Use of undefined constant zen_in_guest_checkout - assumed 'zen_in_guest_checkout'
(this will throw an Error in a future version of PHP) in
...\includes\templates\template_default\pricelist\tpl_main_page.php on line 68.
As reported on the Zen Cart support-thread, the following debug-log results: