The people who use the software of the people who write the software. If the word "customers" is triggering, the argument holds just as well as for "users".

Why are you dodging the question? Who are you talking about, and why?

It's not the commenters above that complained about the error message, they aren't users and highly unlikely to ever become users. Instead you've brought in some unspecified other for unspecified reasons.

I answered all of your questions directly.

No, you did not.