I'm using ss 2.3.7 and ecommerce v0.5.4
I enabled the paypal option by following the instructional documentation here http://doc.silverstripe.org/modules:ecommerce

by adding this to mysite/_config.php
// Define which payment methods your site uses.
Payment::set_supported_methods(array(
   'ChequePayment' => 'Cheque Or Pay On Site',
   'PayPalPayment'   => 'PayPal (Credit Card)'
));

but getting a few errors when trying to configure the rest of paypal with my account information.
The PayPalPayment class thats packaged with the ecommerce plugin doesn't seem to be complete.
There is this old one form about 2 years ago it seems, which I don't think is compatible any more http://open.silverstripe.org/attachment/ticket/1760/PayPalPayment.php

the setup method outlined here is also a little out dated it seems http://www.silverstripe.org/archive/show/196242
the following methods to set your account emails don't exist
if(Director::isLive()) {
   PayPalPayment::set_account_email('info@mysite.com');
} else {
   PayPalPayment::set_test_mode('info@mysite.com');
}

..... It shouldn't be that hard to configure paypal, I'll try and suss it out.