Script:

#!/usr/bin/env perl

use strict;
use warnings;

use Data::Dump;

my $ref = [ map { +{ id => $_ } } qw{a b c b} ];
dd $ref;
my %seen;
@$ref = grep { ! $seen{$_->{id}}++ } @$ref;
dd $ref;
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Output:

[{ id => "a" }, { id => "b" }, { id => "c" }, { id => "b" }]
[{ id => "a" }, { id => "b" }, { id => "c" }]
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