CGI doesn't have the method (start_td etc) that you're using
You need to pass in each value to methods such as td, Tr etc:

#!/usr/bin/perl

use warnings;
use strict;
use CGI qw(:standard);

my $foo = "bar";
my $bar = "baz";

#i've passed Tr an _array reference_
print Tr([td($foo), td($bar)]), "\n";
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You might also want to check out something like HTML::Template or Template::Toolkit

Update: after your update:

print Tr( [ td($req.$key),
            td(input(-type=>$input_html{$key}, -name=>$key))
          ] );
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Should do what you want (untested). However, writing this makes me think that there's a Better Way of doing what you're trying to do.