RuntimeException when patch submission. Module Webform Rest
Ok mate if you open up
webform_rest\Plugin\rest\resource\WebformSubmissionResource.php
and find the patch method you will see
public function patch($webform_id, $uuid, array $webform_data) { ...

looks like Webform Rest 4.0.0-beta1 is now using the submission uuid
so
/webform_rest/{webform_id}/submission/{sid}

&quot;sid&quot; should now be Webform Submission UUID
for the body field or the $webform_data
the module is looking for
  foreach ($webform_data as $field =&gt; $value) {
      $webform_submission-&gt;setElementData($field, $value);
    }

so your json should look like:
   {
    &quot;filed_name&quot;: &quot;value&quot;
   }

because json_decode($json_string, true) will return an array.
if that does not work then file a bug ticket