If the settlement period is inside of one month, then A2X will send only one invoice over to Xero.
Xero will usually automatically detect the matching invoice total and deposit amount, and it will suggest the match in the reconcile screen for you.
If the settlement period spans over two months, A2X creates two invoices and sends them to Xero.
In Xero, you will need to click 'Find & Match' to select the two invoices that correspond to the settlement deposit from Amazon.
If you have a bank account in Xero, in a currency that does not match your Amazon invoices, then please ensure that you've un-checked the 'Show CURRENCY items only' option in the 'Find & Match' reconcile screen.