Solidus has a flexible payments system that allows multiple payment methods to be used during checkout.
The logic for processing payments is decoupled from Solidus's orders system. This allows you to easily define your own payment methods with custom processing logic.
The payments system has many moving parts. The following list summarizes the essential parts of the payments system:
Spree::PaymentMethods
configured. Payment methods send payment information to a payment service
provider.Spree::Payment object is created.Spree::Payments can have a payment source. The source
depends on the payment method that is used. For example, the payment source
could be a Spree::CreditCard, Spree::StoreCredit, or a non-Spree model
provided by your payment service provider integration.Spree::Payment::Processing class calls on
Spree::PaymentMethod and attempts to capture the payment.The complexity of your store's payments system depends on the payment gateways that you use and the amount of payment methods that you need to support.
The rest of this article summarizes these parts of the system.
In order for you to successfully process payments, your Spree::PaymentMethods
need to send information to a 
  
    payment service provider
    
  
 (PSP).
The Solidus community has created a number of Solidus extensions to connect popular PSPs like Braintree, Adyen, Affirm, and Paybright.
Typically, PSP integrations use the Spree::PaymentMethod base class to build
out to the PSP's specifications and API.
Solidus is not built to process payments by itself, and it does not include any integrations for popular PSPs. You must install an extension or create your own integration.
For more information about payment service providers in Solidus, see the Payment service providers article.
In Solidus, each Spree::PaymentMethod represents a way that your store chooses
to accept payments. For example, you may want to set up separate payment methods
for PayPal payments and credit card payments.
Solidus does not include working payment methods by default. Typically, you need to integrate your payment method with a payment service provider .
Solidus includes bogus credit card methods for testing, a basic
Spree::PaymentMethod::CreditCard class that you can use for modeling your own
credit card payment methods, and some other basic payment methods.
For more information, see the Payment methods article.
The Spree::Payment model in Solidus tracks payments. A new payment is created
once the customer has submitted their payment details during checkout.
Payments relate to a specific Spree::Order, as well as one of your available
Spree::PaymentMethods and a payment source (which could be a
Spree::CreditCard, a Spree::StoreCredit or some other non-Spree model).
Note that a payment being created does not mean that a payment has been made
successfully. The Spree::Payment model has a state machine that tracks the
status of a payment. Once the payment is processed by your payment service
provider, the state could become complete, failed, void, and so on.
For more information about payments, see the Payments article.
Each Spree::Payment tracks a payment source. The payment source depends on the
types of payments you accept for each payment method.
For example, if you use Solidus's built-in Spree::PaymentMethod::CreditCard
payment method, the payment source class should always be set to
Spree::CreditCard.
Your payment methods may have more complex payment source classes. For example,
if you use the 
  
    solidus_paypal_braintree
    
  
 gem,
payments made using your Braintree payment methods have the payment source
SolidusPaypalBraintree::Source. However, the SolidusPaypalBraintree::Source
class has a payment_type method that could have a value of ApplePay,
CreditCard or PayPalAccount.
For more information about payment sources, see the Payment methods article.
The Spree::Payment::Processing class's process! method can operate on
completed orders. It attempts to capture orders, invoking the customer's
selected Spree::PaymentMethod and sending payment details to the payment
service provider.
For more information about processing payments, see the Payment processing article.
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