So you have a version that works but did not apply the changes that I suggested. When I mentioned a self-contained example, I meant something like the following below, which does not need any editing to be runnable:

use strict;
use Data::Dumper;

my %REST_storage;

my $json_decoded = {
          'data' => [
                      {
                        'svpIp' => '10.1.1.1',
                        'model' => 'xyz',
                        'storageDeviceId' => '800000058068',
                        'serialNumber' => 58068
                      }
                    ]
        };

            print Dumper $json_decoded;
            for my $key1 (keys %$json_decoded)
            {
                # key1 = data
                print "key 1:  $key1 + $json_decoded->{$key1}\n";
                for my $key2 (keys @{ $json_decoded->{$key1} }) 
                {
                    # key2 = 0 .. x
                    print "key 2:  $key2 + $json_decoded->{$key1}[$key
+2]\n";
                    for my $key3 (keys %{ $json_decoded->{$key1}[$key2
+] }) 
                    {
                        # key3 = storageDeviceId,model,etc
                        print "key 3:  $key3 + $json_decoded->{$key1}[
+$key2]{$key3}\n";
                        $REST_storage{$key3} = $json_decoded->{$key1}[
+$key2]{$key3};
                    }
                }
            }
[download]

That code is explicit about what it uses instead of relying on keys on a reference still working.

Maybe you can look at this code and determine whether it applies to your situation or not. I didn't try this with a recent Perl version.