REST API plugin 1.6.0 unable to add user to groups

Hello,

We are using the REST API plugin in order to add user to groups. The version of plugin is 1.6.0 and the version of OpenFire is 4.6.6, build 5b6b732. We use the POST/users/{username}/groups endpoint.
However we receive an InternalServerError as response. If we update to OpenFire version 4.7.1 and REST api plugin v.1.7.1 the same request is successfully executed.

The request body is:

{
“groupnames”: [
“001”,
“002”
]
}

If instead of the POST/users/{username}/groups endpoint we use the POST /users/{username}/groups/{groupName}, which simply adds a user to a group without having to add a json body, the request is successfully executed in both versions.

If you need any other detail in order to investigate the above behavior please feel free to ask. Any help would be highly appreciated.