Official PayPal Express for Spree
This is the official PayPal Express extension for Spree, based on the extension by PaulCC it has been extended to support Spree's Billing Integrations which allows users to configure the PayPal Express gateway including API login / password and signatures fields via the Admin UI.
This extension allows the store to use PayPal Express from two locations:
Checkout Payment - When configured the PayPal Express checkout button will appear alongside the standard credit card payment options on the payment stage of the standard checkout. The selected shipping address and shipping method / costs are automatically sent to the PayPal review page (along with detailed order information).
Cart Checkout (THIS FEATURE IS NOT YET COMPLETE) - Presents the PayPal checkout button on the users Cart page and redirects the user to complete all shipping / addressing information on PaypPal's site. This also supports PayPal's Instant Update feature to retrieve shipping options live from Spree when the user selects / changes their shipping address on PayPal's site.
This extension follows the documented flow for a PayPal Express Checkout, where a user is forwarded to PayPal to allow them to login and review the order (possibly select / change shipping address and method), then the user is redirected back to Spree to confirm the order. The user MUST confirm the order on the Spree site before the payment is authorized / captured from PayPal (and the order is transitioned to the New state).
Add the following line to your application's Gemfile
gem "spree_paypal_express", :git => "git://github.com/spree/spree_paypal_express.git"
Note: The :git option is only required for the edge version, and can be removed to used the released gem.
Install the gem using Bundler:
Copy & run migrations
bundle exec rails g spree_paypal_express:install
To determine the correct version of this extension, please refer to the Versionfile.
IPN & eCheck Support
eCheck payments are now fully supported and PayPal's Instant Payment Notification service is also supported for receiving updates relating to eCheck payments only. To configure eCheck payments you'll need to:
Configure your PayPal account to accept eCheck payments (under Profile on PayPal's website).
Set the IPN URL on your PayPal account (under Profile on PayPal's website) to:
Enable auto_capture within Spree (as eCheck payments are only supported for purchase and not authorize requests).
Spree::Config.set(:auto_capture => true)
- Before you begin
You'll need to have a Paypal developer account (developer.paypal.com) and both buyer and seller test accounts.
Your sandbox credentials are available from the API Credentials link.
- Setup the Payment Method
Log in as an admin and add a new Payment Method (under Configuration), using following details:
Name: Paypal Express
Environment: Development (or what ever environment you prefer)
Click *Create , and now add your credentials in the screen that follows:
Review: unchecked 
Signature: API signature from your paypal seller test account
Server: test (for Development or live for Production)
Test Mode: checked (or unchecked for Production)
Password: API Password from your paypal seller test account
Login: API Username from your paypal seller test account (care to use the API Username and not the Test Account address)
While testing PayPal Express checkout locally make sure you're logged into your PayPal developer account in another browser window before attempting a PayPal payment, as you'll be redirected and forced to sign in to your developer account.
Add an item to cart
Address step: complete it using a valid US address.
Delivery step: pick anything
On the Payment Step, you should see a PayPal button. You can select it directly or just click "Continue"
You will get redirected to PayPals sandbox site, be sure to log in as a Buyer / Personal test account and not the account you use to configure the Payment Method with.
You should now see the paypal order details screen with a Pay Now button.
Click Pay Now, and you should now be redirected back to Spree's order thank you page.
Log into the Admin UI and review the Order and Payment details to confirm the successful checkout.
Create Test App
To automatically capture funds or enable accepting eCheck payments, add this to you site extension's activate method:
if ::Config.instance ::Config[:auto_capture] = true end
 If you check the review checkbox in the admin section for Payment Methods/Paypal Express, the flow is slightly different. Instead of Pay Now on Paypal's order details page, it now says Continue. And the user is directed back to the spree app's Confirmation page showing a place order button. Use whichever suits your needs best. Personally, I leave review unchecked to cut down on the steps in the checkout flow.