When I try to checkout it gives me a white page with text.

Sandbox/Normal:

Please make sure you are using the right API settings and that you are using the API settings of the selected account type (Normal / Sandbox).

You can find this in the config.php, open the file 

plugins/droppy_premium/config.php

and try to find something called $sandboxFlag make sure that this is set to true when you are in sandbox mode and to false when you are in live mode

E.g.

$sandboxFlag = false;

API Credentials

Make sure your API credentials are set correctly, more info about how to find them can be found over here

Account

Make sure your Paypal account is a business account, else you won’t be able to create any checkouts. More info about a business account can be found here

Price

Make sure that you are not using a comma ( , ) for decimal prices, instead you should use a dot ( . ) for decimal prices. So e.g. 5.99

Latest version

Make sure you are using the latest version of the Premium plugin and Droppy itself.