Xero are currently experiencing issues with their API caused by problems with their service provider AWS. We have suspended sending pay details to Xero until the issues have been resolved which at this stage appears to be a few hours way. When we restart the connection any pays that have been processed in the interim will be sent through to Xero.
For more information on the Xero status, please see their website: https://status.developer.xero.com/
Update, 27 November: The AWS issues continued throughout the day but seemed to have been resolved overnight so this morning we started sending pays to Xero. Any pays created yesterday will have been sent earlier today.