The payment gateway isn't mapped to a Xero fee account
The order synced, but the gateway's processing fee did not. The payment method isn't mapped to a Xero fee account, so there is nowhere for the fee to post.
Map the gateway to a Xero fee account in Setup - Payouts, then re-post the order.
If you don't track gateway fees in Xero, you can turn fees off instead: for that one gateway in Setup - Payouts, or for the whole store in Setup - Advanced.
Recording fees is worth setting up if you haven't - it means your gross sales, your fees and the net amount that reaches your bank all reconcile without manual journals.
Still stuck? Email us at help@hyvelabs.co with your shop URL, the order number and the message shown on the order.