The item cannot be synchronised because the associated bank transaction has been reconciled in Xero. Once a transaction has been reconciled, Expend can no longer make any changes to the expense details associated with it.
It may be possible to unreconcile the transaction. Please consult Xero guidance on this: see https://central.xero.com/s/article/Unreconcile-an-account-transaction.
If the item is unreconciled, you can retry synchronisation by clicking the Sync button on the expense.