while(1)
{

  my $url="https://cucxnpub/vmrest/users?rowsPerPage=2000\&pageNumber=$page";

    $ua = LWP::UserAgent->new(ssl_opts => {
    SSL_verify_mode => IO::Socket::SSL::SSL_VERIFY_NONE,
    verify_hostname => 0,
}); #<<<< $url is OUT of scope

  $header = HTTP::Headers->new;
  $req = HTTP::Request->new(GET => $url); #IF you had "use strict", this would show an error.