We upgraded Umbraco 7 To Umbraco 11 and upgraded Newsletter Studio v2.1.9.8 to v11.0.12.

I dont see an option to add Recipients from the EMAIL section. Reload/Update Recipients is giving following error.

{"errorMsg":"Failed to retrieve data for child nodes undefined","data":{"ExceptionMessage":"Can't create child nodes for id: 79c1c630-cf32-440b-a067-45d9f4b8c12brecipients","ExceptionType":"System.ArgumentException, System.Private.CoreLib, Version=7.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e","StackTrace":" at NewsletterStudio.Core.Backoffice.Trees.TreeService.GetItems(String parentId)\r\n at NewsletterStudio.Web.Backoffice.Trees.NewsletterStudioTreeController.GetTreeNodes(String id, FormCollection queryStrings)\r\n at Umbraco.Cms.Web.BackOffice.Trees.TreeControllerBase.GetTreeNodesAsync(String id, FormCollection queryStrings)\r\n at Umbraco.Cms.Web.BackOffice.Trees.TreeControllerBase.GetNodes(String id, FormCollection queryStrings)\r\n at lambdamethod1295(Closure, Object)\r\n at Microsoft.AspNetCore.Mvc.Infrastructure.ActionMethodExecutor.AwaitableObjectResultExecutor.Execute(ActionContext actionContext, IActionResultTypeMapper mapper, ObjectMethodExecutor executor, Object controller, Object[] arguments)\r\n at Microsoft.AspNetCore.Mvc.Infrastructure.ControllerActionInvoker.

We were able to add subscribers programatically using INewsletterStudioService.