Monthly renewal emails not sent

The monthly renewal emails not sent from Creatio CRM.

The 'Email' step in the process library fails with the below error.

Microsoft.Exchange.WebServices.Data.ServiceRequestException: The request failed. The remote server returned an error: (401) Unauthorized. ---> System.Net.WebException: The remote server returned an error: (401) Unauthorized.

Code used in the business process :

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var invoiceId = Get("CreatedInvoiceId");

var userConnection = Get("UserConnection");

//Terrasoft.Configuration.AimCreateMonthlyInvoiceJob.SendEmail(context.UserConnection, invId);

Terrasoft.Configuration.AimCreateMonthlyInvoiceJob.SendEmail(userConnection, invoiceId);

return true;