I was expecting as mentioned in the link you sent that this particular part of the code would work like a sniffer and decipher more information as to why it fails
Like I said in that link you use $err to get more info about which Unknown Error it is.
You only look if the request fails, and only because "Unknown Error" is diagnostically useless.
$! expands to "Unknown Error" for too many errors, like
(100)(Unknown error)(100)(Cannot create another system semaphore)
(101)(Unknown error)(101)(The exclusive semaphore is owned by another
(102)(Unknown error)(102)(The semaphore is set and cannot be closed)
(103)(Unknown error)(103)(The semaphore cannot be set again)
(104)(Unknown error)(104)(Cannot request exclusive semaphores at inter
(105)(Unknown error)(105)(The previous ownership of this semaphore has
(106)(Unknown error)(106)(Insert the diskette for drive %1)
You're also supposed to look at print $response->dump,"\n";
on error, because it might contain more than "Unknown Error"