Pattern not defined grok error

Hi , I read all the discussions related to custom grok patterns but couldn't find a solution to my issue. I am getting error as:
[2020-06-08T03:00:07,412][ERROR][logstash.javapipeline ] Pipeline aborted due to error {:pipeline_id=>"main", :exception=>#<Grok::PatternError: pattern %{PAYLOAD:payloads} not defined>
Also my config file is as follows:

        file {
                path => "/v/region/*******thread-2.log" 
                start_position => "beginning"


filter {
        grok {
                patterns_dir => [" ***/patterns"]
                match => { "message" => "%{PAYLOAD:payloads}" }
output {
        elasticsearch {
                hosts => "****"
                index => "testindex2"
        stdout { }

My patterns directory contains a file called payload. It's content are as:

PAYLOAD ^payload.*

I meant to store a log line starting with the string payload to my message field.

Please help me with this.
Thanks in advance.