Create User Role & API Call

[simond]

Good day,

i have been trying to create new users using an API call.
To achieve this, I wrote an extension with basically two files
1. application/Espo/Custom/Acl/User.php

<?php
namespace Espo\Custom\Acl;
use \Espo\Entities\User as EntityUser;
use \Espo\ORM\Entity;

class User extends \Espo\Core\Acl\Base {
    public function checkEntityCreate(EntityUser $user, Entity $entity, $data) {
        return $this->checkEntity($user, $entity, $data, 'create');
    }
}
?>

and 2. application/Espo/Resources/metadata/scopes/User.json

{
    "entity": true,
    "layouts": true,
    "tab": true,
    "acl": true,
    "aclActionList": ["create", "read", "edit"],
    "aclActionLevelListMap": {
        "edit": ["all", "own", "no"]
    },
    "customizable": true,
    "object": true
}

I could then assign the "create" permission to a new role and assign this role to a user (and respectively an api user).
However, even in the front-end I cannot create a new user with a non-admin user, having the appropriate role. I can access the form to create a new user, however, I cannot assign either a username, a role or a team (see attached figure).



A call to the REST-API yields a "400 Bad Request" error with "X-Status-Reason →Not valid data. Field: 'userName', type: required.".
My request body looks like this:

{
    "type": "regular",
    "firstName": "fasd",
    "lastName": "fdasd",
    "isActive": true,
    "isSuperAdmin": false,
    "teams": {
        "teamsIds": []
    },
    "gender": "",
    "userName": "mustermann3",
    "salutationName": "Ms.",
    "password": "1qay",
    "passwordPreview": "",
    "passwordConfirm": "1qay",
    "title": null,
    "emailAddressData": [],
    "emailAddress": null,
    "emailAddressIsOptedOut": null,
    "phoneNumberData": [],
    "phoneNumber": null,
    "phoneNumberIsOptedOut": null,
    "defaultTeamName": null,
    "defaultTeamId": null,
    "rolesIds": [],
    "rolesNames": {},
    "teamsIds": [],
    "teamsNames": {},
    "teamsColumns": {}
}

Unfortunately my logging does not seem to work properly, that is why I cannot track the incoming request.
Does anybody have an idea, why this approach does not work or where I can find access permissions for the userName field?

Best wishes and many thanks in advance
Simon