Ok, I'll give them a little credit in that it was actually tax related. Their math wasn't matching because they were adding tax to a tax free line.

But they still literally said to me: I don't understand what this error message means.

When the full error message was:

Calculated tax amount of $$$ does not match listed tax amount of $$$. Please check calculations.

So I still have little sympathy. I found the issue immediately upon checking the tax section

Especially when the email also included a scathing line about how the system never works properly. Why doesn't it ever work right the first time?

Which, yeah, the system does fuck up and get things wrong sometimes, but when it's this person bringing us an issue it's 98% of the time a user issue.

Because they basically never read the message the computer is giving. They just screen shot and send into us.

(also I did tell them the real issue, but I so wanted to play dumb at the same time)