End of script output before headers: converter.cgi

I have this same problem and I already verified the syntax of the Perl script and I see that everything is correct, I do not understand the reason why it does not work. Here is the layout of the form:

<form id="formu" action="convertidor.cgi" method="POST" class="form register">
    <h2 class="form_titulo"> Convertidor de temperaturas </h2>
    <div class="contenedor-inputs">
        <br>
        <input type="text" name="grados"  id="nombre" placeholder="Ingresa el número de grados  " maxlength="10" class="input-100" required  />
        <center>
            <input type="radio" name="conver" id="CF" value="CF" checked>
            <label for="CF">Celsius a farenheit</label>
            <input type="radio" name="conver" id="CK" value="CK">
            <label for="CK">Celsius a Kelvin</label>
            <input type="radio" name="conver" id="FC" value="FC">
            <label for="FC">Farenheit a celsius</label>
            <input type="radio" name="conver" id="FK" value="FK">
            <label for="FK">Farenheit a kelvin</label>
            <br>
            <input type="radio" name="conver" id="KF" value="KF" >
            <label for="KF">Kelvin a celsius</label>
            <input type="radio" name="conver" id="KC" value="KC">
            <label for="KC">kelvin a celsius</label>
        </center>
        <center>
            <input class="form-btn" type="submit" id="btnenviar" value="Ingresar" />
        </center>
    </div>

and here the Perl script using the CGI module:

#!"C:\xampp\perl\bin\perl.exe"

use strict;
use CGI;

my $cgi = new CGI;

my $n1 = $cgi->param('grados');
my $op = $cgi->param('conver');

if ($n1 !~ /[0-9]+$/) {
    print $cgi->header("text/html");
    print "Error ha ingresado datos incorrectos";
    return;
}

my $total;

if ($op eq "CF") {
    $total = (9*$n1)/5+32;
}
elsif ($op eq "CK") {
    $total = $n1+273.15;
}
elsif ($op eq "FC") {
    $total = 5*($n1-32)/9;
}
elsif ($op eq "FK") {
    $total = (5*($n1-32)/9)+273.15;
}
elsif ($op eq "KC") {
    $total = 9($n-273.15)/5+32
}
elsif ($op eq "KF") {
    $total = $n1-273.15
}

print $cgi->header("text/html");
print $total;