Undefined constant TOPMOST_CATEGORY_PARENT_ID

[celextel108]

Dear Friends,

We are currently using Zen Cart 1.5.8 under PHP 8.1.9 Version at www.celextel.com.

We are getting Blank Page when we try to change the Currency in any Product Info Page.

Example URL:
https://www.celextel.com/?currency=I..._id=76&cPath=5

Debug Log File is showing the following Logs:

[03-Nov-2022 11:08:45 Asia/Kolkata] PHP Fatal error: Uncaught Error: Undefined constant "TOPMOST_CATEGORY_PARENT_ID" in /home/xxxx/public_html/includes/functions/functions_categories.php:186
Stack trace:
#0 /home/xxxx/public_html/includes/classes/usu.php(907): zen_get_parent_categories()
#1 /home/xxxx/public_html/includes/classes/usu.php(715): usu->get_full_cPath()
#2 /home/xxxx/public_html/includes/classes/usu.php(642): usu->get_category_name()
#3 /home/xxxx/public_html/includes/classes/usu.php(387): usu->get_product_name()
#4 /home/xxxx/public_html/includes/classes/usu.php(226): usu->parse_parameters()
#5 /home/xxxx/public_html/includes/classes/observers/UsuObserver.php(55): usu->href_link()
#6 /home/xxxx/public_html/includes/classes/traits/NotifierManager.php(87): UsuObserver->update()
#7 /home/xxxx/public_html/includes/functions/html_output.php(18): base->notify()
#8 /home/xxxx/public_html/includes/init_includes/init_currencies.php(39): zen_href_link()
#9 /home/xxxx/public_html/includes/autoload_func.php(40): require_once('/home/xxxx/...')
#10 /home/xxxx/public_html/includes/application_top.php(237): require('/home/xxxx/...')
#11 /home/xxxx/public_html/index.php(25): require('/home/xxxx/...')
#12 {main}
thrown in /home/xxxx/public_html/includes/functions/functions_categories.php on line 186

We have not made changes to any of these Files.

We do not find Configuration Setting for the following in DB:
TOPMOST_CATEGORY_PARENT_ID

Please guide us as to what to do in this regard.

Thanks,

Lakshmanan