First, make sure that your Billease payment channel has been activated.
To activate the Billease payment channel, please send a request to Xendit's Customer Success Team at help@xendit.ph.
If the Billease payment channel has been activated and still does not appear on your payment link, please follow the steps found our Help Guide Article: I have enabled the payment channel but it does not appear on my invoice, what’s wrong?
Further, if it continues not to appear on your invoice, ensure that you select and fill in "Show order items in the Order Details" (even if the item is only one) during the Payment Link Creation.
You may refer to our documentation here for more guidance.