Why can't you log the variable? Can you compare the variable to a string? Can you run a regex match on it?

yes, run a regex on your received data or, simpler/faster, check if each byte received is ASCII digit (0x30-0x39). However, you have a huge data verification task ahead if your device behaves like this...

I can't log the variable because as I explain is not happened every time.

The two aren't related. You can easily log something that doesn't happen every time:

use warnings;
use strict;
use Data::Dumper;
$Data::Dumper::Useqq=1;
my $count = 0;
for (1..100) {
    my $string = ("0\x04\x88\x80\x80\x80\x86\x98\x050", "7630001998")[
+ (rand()<0.1) ? 0 : 1 ];
    if($string =~ /[^0-9]/) {
        print STDERR "Warning, weird string #", ++$count, " on run #$_
+ at ", scalar localtime, ": ", Dumper($string);
    }
}

__END__
Warning, weird string #1 on run #7 at Wed Mar 11 08:59:53 2020: $VAR1 
+= "0\4\210\200\200\200\206\230\0050";
Warning, weird string #2 on run #16 at Wed Mar 11 08:59:53 2020: $VAR1
+ = "0\4\210\200\200\200\206\230\0050";
Warning, weird string #3 on run #30 at Wed Mar 11 08:59:53 2020: $VAR1
+ = "0\4\210\200\200\200\206\230\0050";
Warning, weird string #4 on run #36 at Wed Mar 11 08:59:53 2020: $VAR1
+ = "0\4\210\200\200\200\206\230\0050";
Warning, weird string #5 on run #37 at Wed Mar 11 08:59:53 2020: $VAR1
+ = "0\4\210\200\200\200\206\230\0050";
Warning, weird string #6 on run #46 at Wed Mar 11 08:59:53 2020: $VAR1
+ = "0\4\210\200\200\200\206\230\0050";
Warning, weird string #7 on run #54 at Wed Mar 11 08:59:53 2020: $VAR1
+ = "0\4\210\200\200\200\206\230\0050";
Warning, weird string #8 on run #60 at Wed Mar 11 08:59:53 2020: $VAR1
+ = "0\4\210\200\200\200\206\230\0050";
Warning, weird string #9 on run #71 at Wed Mar 11 08:59:53 2020: $VAR1
+ = "0\4\210\200\200\200\206\230\0050";
Warning, weird string #10 on run #95 at Wed Mar 11 08:59:53 2020: $VAR
+1 = "0\4\210\200\200\200\206\230\0050";
Warning, weird string #11 on run #96 at Wed Mar 11 08:59:53 2020: $VAR
+1 = "0\4\210\200\200\200\206\230\0050";
Warning, weird string #12 on run #98 at Wed Mar 11 08:59:53 2020: $VAR
+1 = "0\4\210\200\200\200\206\230\0050";
[download]

Notice the "weird" event happens only ~10% of the time, but it can datalog just fine. Use whatever logging system you have in place, rather than STDERR, in your application.

If the issue happens that infrequently then logging the error with as much context you can provide is the most sensible thing you can do.

The best fix is correcting the issue rather than dropping data on the floor and retrying. The worrying thing is that if you can get obvious corruption of messages you may also be able to get subtle corruption that looks OK to your tests on the receiving end, but is wrong. If you have control over both ends of the link you could change the message format to include error checking so that you have reasonable confidence that your data is reliable.

This is not a problem that we can sensibly help with without a lot more context. In the worst case this sort of problem can kill people and in some jurisdictions we could be held libel as a result of giving you unfortunate advice.

Optimising for fewest key strokes only makes sense transmitting to Pluto or beyond

I don't think problem is in device, probably something with ENV. The script is simple:

use strict;
use warnings;
use Device::SerialPort;
use HTTP::Tiny;

sub send_msg {
    my ($self, $enccmd) = @_;
    my $pass = $oPrinter->write($enccmd) || return "Cannot communicate
+ with Fiscal printer !";
    my $timeout = 1;
    $oPrinter->read_char_time(0);
    $oPrinter->read_const_time(200);
# Read_Total = read_const_time + (read_char_time * bytes_to_read)
    my $chars = 0;
    my $buffer = "";

    while ($timeout > 0)
    {
        my ($count, $saw) = $oPrinter->read(1);
        if ($count > 0)
        {
            if (ord($saw) != 22)
            {
                $chars += $count;
                $buffer .= $saw;
            }
        } else {
            $timeout--;
        }
    }
    return $buffer;
}

my $test = $self->send_msg("\r\nGET NEW DATA\r\n");

    my $url = "$self->{HOST}/report.php?fnac=";
    $url .= "$self->{unic}&num=";
    $url .= "$test";
    my $response = HTTP::Tiny->new->get($url);
[download]

I saw something like this string "\x33\x35" on other project and I start thinking may be the problem is how data is delivered, like error how data is parsed or send and parsed like php urlencode something like that. I also because never see such a value in variable, don't know how is present there. Any suggestion ?