Error when installing the shipping surcharge module

[Semi-Crazy]

I've followed the instructions for unzipping and uploading the files for the shipping surcharge module and it shows up in the "Order Totals Modules" list.

Unfortunately when I click on it so the right hand side bar with the “Install” button should show up all I get is the partial list of the "Order Totals Modules" that shows above the shipping surcharge module. I see nothing of the list that should be below and no right hand side bar were the ”Install” button should be.

Image A


Image B


Here is the debug log file that I get with it. (I've replaced admin folder name and IP address with *)

[06-Mar-2022 19:35:54 UTC] PHP Fatal error: Uncaught Error: Call to a member function Execute() on null in /includes/modules/order_total/ot_shippingsurcharge.php:115
Stack trace:
#0 /*********/modules.php(218): ot_shippingsurcharge->keys()
#1 /*********/index.php(11): require('/nfs/home4/home...')
#2 {main}
thrown in /includes/modules/order_total/ot_shippingsurcharge.php on line 115

[06-Mar-2022 19:35:54 UTC] Request URI: /*********/index.php?cmd=modules&set=ordertotal&module=ot_shippingsurcharge, IP address: ***.**.**.**
--> PHP Fatal error: Uncaught Error: Call to a member function Execute() on null in /includes/modules/order_total/ot_shippingsurcharge.php:115
Stack trace:
#0 /*********/modules.php(218): ot_shippingsurcharge->keys()
#1 /*********/index.php(11): require('/nfs/home4/home...')
#2 {main}
thrown in /includes/modules/order_total/ot_shippingsurcharge.php on line 115.

Thanks for any help that anyone can provide. I'm just a beginner at this coding stuff.