How to make work Restfull /user/register?_format=hal_json I am trying to access. All required modules are included, rights granted. so does not work.
/user/register?_format=hal_json

I get a message:

{"message":"Not acceptable format: hal_json"}


In RestUi settings, hal_json format is enabled. 

And in the log:

Symfony\Component\HttpKernel\Exception\NotAcceptableHttpException: Not acceptable format: hal_json in Drupal\Core\EventSubscriber\RenderArrayNonHtmlSubscriber-&gt;onRespond() (line 30 of .../web/core/lib/Drupal/Core/EventSubscriber/RenderArrayNonHtmlSubscriber.php).


Drupal 9.0 and Drupal 8.8.4
please add at header:
 Content-Type : application/hal+json