Forum Post: RE: connection to crm online API by user of office 365

try adding device name and device Password with your CRM connection string. if (Org.Host.ToLower().Contains("dynamics.com")) { crmConnection .DeviceCredentials = new System.ServiceModel.Description.ClientCredentials(); crmConnection .DeviceCredentials.UserName.UserName = DeviceId; crmConnection .DeviceCredentials.UserName.Password = DevicePassword; }