decode_json is a function. It returns the data structure and does not modify its argument in place. You might want:

my $foo;
my $ok= eval {
    $foo= decode_json( $foo_info );
    1;
};
if( ! $ok ) {
    my $err= $@;
    flash error => "Failed";
    warn "JSON Decoder got '$err'";
};

# Now we have the decoded data structure in $foo
warn Dumper $foo;
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