Last year, my Adsense account was upgraded to the new AdSense payments platform. As part of this change, Google will be shutting down the old payments platform completely by the end of this month.
What this simply means is that by June 30, 2015, your payments data prior to the upgrade date (Mar-2014 in my own case) will no longer be available.
So, Google recommends that you download your data and save a copy in case you need it in the future, e.g., for tax purposes.
To download your old payments data, please follow the steps below:
==> Sign in to your AdSense account.
==> Click the gear icon and select Payments.
==> Scroll down to the "Previous payments" section at the bottom of the page.
==> Click "See your previous payments".
==> In the "Finalized earnings and payments" section, click Export to CSV.
==> If a download prompt appears, follow the instructions in the dialog, and click Save and it will be downloaded as a CSV file.
Note that if you don't see the "See your previous payments" button, then you don't have any previous payments data on our old payments system to download.
I hope this helps.