If some data are not synced to Xero it is possible to synchronise invoices and payments over past dates.
The synchronisation can be done by
1. Go to Setup > Connections > Integrations > Configure Xero.
2. Click on the Xero account to access the setup page.
3. Click on the Tools tab.
4. Select the Dates From and To.
5. Click Enqueue Request.
It can take a few hours for the data to be synced.