If you have a loan from Amazon, the initial receipt of those loaned funds and payments to that loan are likely to show up in your settlements in A2X.
As A2X does not have access to the details of your loan, the split between principal and interest does not show up in your settlements. As this is the case, the amount of interest will need to be split out from the total Amazon Lending payment amount in your accounting system to record the expense.
This is usually done by entering a journal entry at the end of each month to reduce the loan by the interest expense amount. A monthly loan statement should provide information on this breakdown of interest and principal. Be sure to get a knowledgeable professional to enter journals if you are not familiar or comfortable doing them yourself.
See this Blog post for more information on Amazon Lending:
Amazon Lending Has Funded 20,000 Businesses