IO::Async::Process exit code 256? Why?

.pl

#!/usr/bin/env perl

use v5.36;
use IO::Async::Loop ();
use IO::Async::Process ();
use IO::Async::Timer::Periodic ();

my $loop = IO::Async::Loop->new;

my $timer = IO::Async::Timer::Periodic->new(
    interval => 1,
    on_tick  => sub {
        say "You've had 1 second (" . time() . ')';
        my $proc = IO::Async::Process->new(
            code => sub { say 'Hello?' },
            on_finish => sub {
                my ( $self, $exitcode ) = @_;
                print "Process finished with code $exitcode\n";
            },
        );
        $loop->add($proc);
    },
);

$loop->add($timer);

$timer->start;

$loop->run;