There are a couple issues. One is that you had references and you treated one as a hash. Also, I think you meant "key" when you used $key (of course, if $key eq "key"...).

This code seems to work.

use strict;
use warnings;

{
    foreach my $datum (@{$var1->{"key"}->{"data"}->[0]})
    {
        print "$datum\n";
    }
}
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