502 Bad Gateway message while adding a tracking number

Hello there,

While adding a tracking number on a new order i got this error on a slide in message box on left corner.

502 Bad Gateway Bad Gateway Web server received an invalid response while acting as a gateway or proxy server. Web Server at domain.com

After refreshing the page i can see that the tracking is succesfully added.

But this message is annoying and would like to get rid of it.

Any clues about this message would be greatly appreciated.

Best Regards,