D8 RESTful POST Route Not Found Error

Need to migrate Rest services custom module, that processes POST requests, from drupal 7 to 8. The GET works by following instructions in https://www.drupal.org/docs/8/api/restful-web-services-api/custom-rest-r.... But can't get POST to work, route not found error.

The GET is working, but POST give path error.

drupal-8.8.4

---

<code>
/modules/custom/tax_tob/config/install/rest.resource.demo_resource.yml

id: Demo_resource
plugin_id: Demo_resource
granularity: method
configuration:
  GET:
    supported_formats:
      - json
    supported_auth:
      - basic_auth

  POST:
    supported_formats:
      - json
      - hal_json
    supported_auth:
      - basic_auth

---
/modules/custom/DemoApi/src/Plugin/rest/resource/DemoResource.php
<?php

namespace Drupal\DemoApi\Plugin\rest\resource;

use Drupal\rest\Plugin\ResourceBase;
use Drupal\rest\ResourceResponse;

/**
 * Provides a Demo Resource
 *
 * @RestResource(
 *   id = "Demo_resource",
 *   label = @Translation("Demo Resource"),
 *   uri_paths = {
 *     "canonical" = "/DemoAPi/Demo_resource"
 *   }
 * )
 */
class DemoResource extends ResourceBase {

  /**
   * Responds to entity GET requests.
   * @return \Drupal\rest\ResourceResponse
   */
  public function get() {
    $response = ['message' => 'Hello, this is a rest service GET'];
    return new ResourceResponse($response);
  }

  /**
   * Responds to entity POST requests.
   * @return \Drupal\rest\ResourceResponse
   *
   * @param mixed $data
   *   Data payload.
   */
  public function post(Array $data) {
    $response = ['message' => 'Hello, this is a rest service POST'];
    return new ResourceResponse($response);
  }
  
}

</code>

error:
'No route found for "POST /DemoApi/Demo_resource"'
 

DEBUG:requests.packages.urllib3.connectionpool:"POST /DemoAPi/Demo_resource?_format=json HTTP/1.1" 404 76
Rcv payload : {u'message': u'No route found for "POST /DemoAPi/Demo_resource"'}