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btw please package and submit to plugins once you have it working.

$ib issue
original file admin/recover_cart_sales.php" line 356 add
$ib = 0;

strtotime issue
That value should not be null but I guess it is so you will want to change

original file...

Your line numbers don't correspond to the latest download - are you working with the last version of the plugin?
This mod hasn't been upgraded for PHP 8.1 yet - you might be better off to go down...

Undefined key warning:

https://docs.zen-cart.com/user/upgrading/php_warnings/#undefined-array-key

Attention all developers, especially those just getting started:

The community needs volunteers to step up and adopt plugins like this. It's a great way to help the project and to build your...

Maybe look at the Admin Notes mod - could be adapted for your need.
https://www.zen-cart.com/downloads.php?do=file&id=847

Has anyone looked at automating sending the emails? Seems like this would be a nice enhancement.