Can you show us your sample confi file?

I am also using YAML file config with same keys, I used to read all the keys as array of hashes.

use strict;
use warnings;
use YAML::XS qw/LoadFile/;
use Data::Dumper;
my $config = LoadFile('./config.yaml');

print Dumper($config);
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Test.yaml

---
- emailName: ree
- emailAddresses:
    - test@test.com
    - user@domain.com
- credential:
    username: user1
    password: password
- credential:
    username: vinothg
    password: password
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But in your case, you expect the module has to say error on duplicate keys?