use strict;
use warnings;
use Dancer;
use JSON qw(decode_json);

my $foo_info = param('foo_info');
if ( !eval { decode_json($foo_info); 1 } )  {
    flash error => "Failed"
}

if ( !exists $foo_info->{foo_total}
    || !($foo_info->{foo_total} =~ m/^\$\d+\.\d{2}$/)) {
        error("Invalid or missing foo info");
        return 0;
}

##</code><code>##

Error decoding json data:
 malformed JSON string, neither tag, array, object, number, string or atom, at character offset 0 (at the line I'm decoding the json)
request to POST /path/to/site crashed: Can't use string .. (json data spit out here) as a HASH ref