Having purchased the plugin and received your license key you will need to download the latest version from the download centre using the link provided in the email receipt.
Once installed in Blesta, you will need a TOKEN to connect to your Xero instance.
Visit the Xero Developer Centre and create a new Web App
You will need to supply the "Redirect URI" which can be found in the Xero Sync settings pane (Tools -> Xero Sync -> Configuration)
Paste these tokens into the configuration page and click the Save button. The page will refresh and you will be able to personalise the settings for your Blesta instance.