Hi Mohamed,
Usually, when you call a REST service and get a HTTP 500 Internal Server Error as a response, it means that something has gone wrong with handling your request, but it has gone wrong at the place where you have sent your request to.
The response that you've added doesn't really give useful information about what has gone wrong. I would suggest checking the documentation of the REST service that you're calling, looking for examples that the owner of the REST service might have provided somewhere, or get in contact with the party that is publishing the REST service.
Greetings Martin