Unable to get users on federation. server indicator is yellow not green. nextcloud 18.0.4

I have tried fresh installation of the server as well but it is still not working.

image

kindly guide me what is the issue or how can I resolve it.

log error:
[no app in context] Error: InvalidArgumentException: Invalid Federated Cloud ID at <>

  1. /var/www/html/nextcloud/lib/private/Collaboration/Collaborators/RemoteGroupPlugin.php line 61
    OC\Collaboration\Collaborators\RemoteGroupPlugin->splitGroupRemote(“spark@”)
  2. /var/www/html/nextcloud/lib/private/Collaboration/Collaborators/Search.php line 65
    OC\Collaboration\Collaborators\RemoteGroupPlugin->search(“spark@”, 200, 0, OC\Collaboration … {})
  3. /var/www/html/nextcloud/apps/files_sharing/lib/Controller/ShareesAPIController.php line 221
    OC\Collaboration\Collaborators\Search->search(“spark@”, [0,1,4,6,9,10], false, 200, 0)
  4. /var/www/html/nextcloud/lib/private/AppFramework/Http/Dispatcher.php line 170
    OCA\Files_Sharing\Controller\ShareesAPIController->search(“spark@”, “folder”, 1, 200, [“0”,“1”,“6”,“9”,“7”,“10”,“8”,“4”], false)
  5. /var/www/html/nextcloud/lib/private/AppFramework/Http/Dispatcher.php line 99
    OC\AppFramework\Http\Dispatcher->executeController(OCA\Files_Sharin … {}, “search”)
  6. /var/www/html/nextcloud/lib/private/AppFramework/App.php line 125
    OC\AppFramework\Http\Dispatcher->dispatch(OCA\Files_Sharin … {}, “search”)
  7. /var/www/html/nextcloud/lib/private/AppFramework/Routing/RouteActionHandler.php line 47
    OC\AppFramework\App::main(“OCA\Files_Shar … r”, “search”, OC\AppFramework\ … {}, {_route: "ocs.fi … "})
  8. <>
    OC\AppFramework\Routing\RouteActionHandler->__invoke({_route: "ocs.fi … "})
  9. /var/www/html/nextcloud/lib/private/Route/Router.php line 299
    call_user_func(OC\AppFramework\ … {}, {_route: "ocs.fi … "})
  10. /var/www/html/nextcloud/ocs/v1.php line 82
    OC\Route\Router->match("/ocsapp/apps/fi … s")

GET /nextcloud/ocs/v1.php/apps/files_sharing/api/v1/sharees?format=json&itemType=folder&search=spark@&lookup=false&perPage=200&shareType[]=0&shareType[]=1&shareType[]=6&shareType[]=9&shareType[]=7&shareType[]=10&shareType[]=8&shareType[]=4
from 84.215.58.0 by spark at 2020-05-17T15:02:37+00:00