If you receive an automated email from Re-Leased with the subject "Billing Contact for Tenancy was Archived" it means the contact associated with the tenancy specified in the email has been archived.
If any invoices are produced for the archived contact a sync error will occur. The message will state that a problem occurred syncing invoices with Xero and contain this text:
Issue: Xero has rejected this approve request with the following message: The contact with the specified contact details has been archived. The contact must be un-archived before creating new invoices or credit notes.
Example sync message:
Any invoices connected to archived contacts will appear in the 'Drafts' section of the Income and Expenses page. Edit the contact on the invoice and save it as approved or awaiting approval to sync it with Xero.
This could have happened by either archiving or merging the contact in Xero. If the contact was merged there will be a current version of them available to connect the Re-Leased tenancy to.
To correct contacts linked to the tenancy, search the tenancy mentioned in the message, then go to Tenancy Details on the left menu. Clear out the name against the Xero Invoice contact and re-type it so that it matches the current version of this contact.