Add a certificate to local user via Management API Web Services

[Res]

Hello,

I'm trying to add a certificate (registration key) to a user via the management api.

But everytime i get an error.

This is my request body

{
 "certificates" :  {
       "add" : {
           "registration-key":{}
       }
   },
 "uid" : "<removed>",
 "details-level" : "full"
}

As a response i get:

{
	"code": "generic_error",
	"message": ""
}

How do a add a certificate to a local checkpoint user?

Thanks in advance!!