Hi, you should not be mucking around with HTTP::Message directly. From the doc for HTTP::Request:

$r->content( $bytes ) This is used to get/set the content and it is inherited from the HTTP::Message base class. See HTTP::Message for details and other methods that can be used to access the content. Note that the content should be a string of bytes. Strings in perl can contain characters outside the range of a byte. The Encode module can be used to turn such strings into a string of bytes.

(You are passing an object, not a string of bytes.)

See also https://metacpan.org/pod/HTTP::Request#Simple-POST.

Hope this helps!