"Customer Download Failure"

Site URL : namobuddhapub.org
ZC version 1.5.8a
Plugins : Square Web Pay...
PHP Version : 8.1 and 8.2
Hosted with DreamHost ( managed hosting )

The owner of store has gotten lots of emails from the store titled :
"Customer Download Failure"
with the following content text in the message ( normal head and foot )
"Customer Download Failure
$EMAIL_MESSAGE_HTML"

I looked through the code, and did not discover what causes this error -
where the message text isn't being presented so it's hard to trace.

I have however in the hopes of resolving them changed the following :
includes/languages/english/lang.download.php
where I remarked out the normal line and instead have added this line :
"
'ERROR_CUSTOMER_DOWNLOAD_FAILURE' => 'Customer Download Failure ' . $_SERVER['REMOTE_ADDR'] ,
"
So now the emails are displaying the IP causing the issue.

In the first of these that the owner has sent me the IP address
is not an IP related to an order in the database.

So I'm posting here as this may be related to some abuses.
It would be good to see the Zen Cart store's code show proper error
instead of saying ( what appears to be broken ) vague error message
" $EMAIL_MESSAGE_HTML "

I checked the forum, and did see this old thread there, but it is closed now :
https://www.zen-cart.com/showthread.php?170614-Customer-Download-Error&highlight=Customer+Download+Failure
If it were not closed, I would post my work around to get their IP.
I do however given the age of that thread that this problem may
be an old issue that's been around many years in ZenCart's code base.