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How to Create a Payment Processor

In this document, you’ll learn how to create a Payment Processor in your Medusa backend. If you’re unfamiliar with the Payment architecture in Medusa, make sure to check out the overview first.

Overview​

A Payment Processor is the payment method used to authorize, capture, and refund payment, among other actions. An example of a Payment Processor is Stripe.

By default, Medusa has a manual payment provider that has minimal implementation. It can be synonymous with a Cash on Delivery payment method. It allows store operators to manage the payment themselves but still keep track of its different stages on Medusa.

A payment processor is a service that extends the AbstractPaymentProcessor and implements its methods. So, adding a Payment Processor is as simple as creating a service file in src/services. The file's name is the payment processor's class name as a slug and without the word Service. For example, if you're creating a MyPaymentService class, the file name is src/services/my-payment.ts.

import { AbstractPaymentProcessor } from "@medusajs/medusa";

class MyPaymentService extends AbstractPaymentProcessor {
  // methods here...
}

export default MyPaymentService

The methods of the payment processor are used at different points in the Checkout flow as well as when processing an order after it’s placed.

Checkout Flow - Payment

Identifier Property​

The PaymentProvider entity has 2 properties: id and is_installed. The identifier property in the payment processor service is used when the payment processor is added to the database.

The value of this property is also used to reference the payment processor throughout Medusa. For example, it is used to add a payment processor to a region.

class MyPaymentService extends AbstractPaymentProcessor {
  static identifier = "my-payment"
  // ...
}

PaymentProcessorError​

Before diving into the methods of the Payment Processor, you'll notice that part of the expected return signature of these method includes PaymentProcessorError.

interface PaymentProcessorError {
  error: string
  code?: string
  detail?: any
}

While implementing the Payment Processor's methods, if you need to inform the Medusa core that an error occurred at a certain stage, return an object having the attributes defined in the PaymentProcessorError interface.

For example, the Stripe payment processor has the following method to create the error object, which is used within other methods:

abstract class StripeBase extends AbstractPaymentProcessor {
  // ...
  protected buildError(
    message: string,
    e: Stripe.StripeRawError | PaymentProcessorError | Error
  ): PaymentProcessorError {
    return {
      error: message,
      code: "code" in e ? e.code : "",
      detail: isPaymentProcessorError(e)
        ? `${e.error}${EOL}${e.detail ?? ""}`
        : "detail" in e
        ? e.detail
        : e.message ?? "",
    }
  }

  // used in other methods
  async retrievePayment(
    paymentSessionData: Record<string, unknown>
  ): Promise<
    PaymentProcessorError |
    PaymentProcessorSessionResponse["session_data"]
  > {
    try {
      // ...
    } catch (e) {
      return this.buildError(
        "An error occurred in retrievePayment",
        e
      )
    }
  }
}

constructor​

You can use the constructor of your Payment Processor to have access to different services in Medusa through dependency injection.

You can also use the constructor to initialize your integration with the third-party provider. For example, if you use a client to connect to the third-party provider’s APIs, you can initialize it in the constructor and use it in other methods in the service.

Additionally, if you’re creating your Payment Processor as an external plugin to be installed on any Medusa backend and you want to access the options added for the plugin, you can access it in the constructor. The options are passed as a second parameter.

Example​

class MyPaymentService extends AbstractPaymentProcessor {
  // ...
  constructor(container, options) {
    super(container)
    // you can access options here

    // you can also initialize a client that
    // communicates with a third-party service.
    this.client = new Client(options)
  }
  // ...
}

Parameters​

containerRecord<string, unknown>Required
An instance of MedusaContainer that allows you to access other resources, such as services, in your Medusa backend through dependency injection
configRecord<string, unknown>
If this fulfillment provider is created in a plugin, the plugin's options are passed in this parameter.

Methods​

capturePayment​

This method is used to capture the payment amount of an order. This is typically triggered manually by the store operator from the admin.

This method is also used for capturing payments of a swap of an order, or when a request is sent to the Capture Payment API Route.

You can utilize this method to interact with the third-party provider and perform any actions necessary to capture the payment.

Example​

import {
  PaymentProcessorError,
  // ...
} from "@medusajs/medusa"
// ...

class MyPaymentService extends AbstractPaymentProcessor {
  // ...
  async capturePayment(
    paymentSessionData: Record<string, unknown>
  ): Promise<Record<string, unknown> | PaymentProcessorError> {
    const paymentId = paymentSessionData.id

    // assuming client is an initialized client
    // communicating with a third-party service.
    const captureData = this.client.catch(paymentId)

    return {
      id: paymentId,
      ...captureData
    }
  }
}

Parameters​

paymentSessionDataRecord<string, unknown>Required
The data field of the Payment for its first parameter.

Returns​

PromisePromise<Record<string, unknown> | PaymentProcessorError>Required
Either an error object or a value that's stored in the data field of the Payment.

authorizePayment​

This method is used to authorize payment using the Payment Session of an order. This is called when the cart is completed and before the order is created.

This method is also used for authorizing payments of a swap of an order and when authorizing sessions in a payment collection. You can interact with a third-party provider and perform any actions necessary to authorize the payment.

The payment authorization might require additional action from the customer before it is declared authorized. Once that additional action is performed, the authorizePayment method will be called again to validate that the payment is now fully authorized. So, make sure to implement it for this case as well, if necessary.

Once the payment is authorized successfully and the Payment Session status is set to authorized, the associated order or swap can then be placed or created. If the payment authorization fails, then an error will be thrown and the order will not be created.

Note

The payment authorization status is determined using the getPaymentStatus method. If the status is requires_more, then it means additional actions are required from the customer. If you try to create the order with a status that isn't authorized, the process will fail.

Example​

import {
  PaymentProcessorError,
  PaymentSessionStatus,
  // ...
} from "@medusajs/medusa"
// ...

class MyPaymentService extends AbstractPaymentProcessor {
  // ...
  async authorizePayment(
    paymentSessionData: Record<string, unknown>,
    context: Record<string, unknown>
  ): Promise<
    PaymentProcessorError |
    {
      status: PaymentSessionStatus;
      data: Record<string, unknown>;
    }
  > {
    try {
      await this.client.authorize(paymentSessionData.id)

      return {
        status: PaymentSessionStatus.AUTHORIZED,
        data: {
          id: paymentSessionData.id
        }
      }
    } catch (e) {
      return {
        error: e.message
      }
    }
  }
}

Parameters​

paymentSessionDataRecord<string, unknown>Required
The data field of the payment session.
contextRecord<string, unknown>Required
The context of the authorization. It may include some of the following fields:
  • ip: The customer’s IP.
  • idempotency_key: The Idempotency Key that is associated with the current cart. It is useful when retrying payments, retrying checkout at a failed point, or for payments that require additional actions from the customer.
  • cart_id: The ID of a cart. This is only during operations like placing an order or creating a swap.

Returns​

PromisePromise<PaymentProcessorError | object>Required
The authorization details or an error object.

cancelPayment​

This method is used to cancel an order’s payment. This method is typically triggered by one of the following situations:

  1. Before an order is placed and after the payment is authorized, an inventory check is done on products to ensure that products are still available for purchase. If the inventory check fails for any of the products, the payment is canceled.
  2. If the store operator cancels the order from the admin.
  3. When the payment of an order's swap is canceled.

You can utilize this method to interact with the third-party provider and perform any actions necessary to cancel the payment.

Example​

import {
  PaymentProcessorError,
  // ...
} from "@medusajs/medusa"
// ...

class MyPaymentService extends AbstractPaymentProcessor {
  // ...
  async cancelPayment(
    paymentSessionData: Record<string, unknown>
  ): Promise<Record<string, unknown> | PaymentProcessorError> {
    const paymentId = paymentSessionData.id

    // assuming client is an initialized client
    // communicating with a third-party service.
    const cancelData = this.client.cancel(paymentId)

    return {
      id: paymentId,
      ...cancelData
    }
  }
}

Parameters​

paymentSessionDataRecord<string, unknown>Required
The data field of the Payment.

Returns​

PromisePromise<Record<string, unknown> | PaymentProcessorError>Required
Either an error object or a value that's stored in the data field of the Payment.

initiatePayment​

This method is called either if a region has only one payment provider enabled or when a Payment Session is selected, which occurs when the customer selects their preferred payment method during checkout.

It is used to allow you to make any necessary calls to the third-party provider to initialize the payment. For example, in Stripe this method is used to create a Payment Intent for the customer.

Example​

import {
  PaymentContext,
  PaymentSessionResponse,
  // ...
} from "@medusajs/medusa"

class MyPaymentService extends AbstractPaymentProcessor {
  // ...
  async initiatePayment(
    context: PaymentProcessorContext
  ): Promise<
    PaymentProcessorError | PaymentProcessorSessionResponse
  > {
    // assuming client is an initialized client
    // communicating with a third-party service.
    const clientPayment = await this.client.initiate(context)

    return {
      session_data: {
        id: clientPayment.id
      },
    }
  }
}

Parameters​

contextPaymentProcessorContextRequired
The context of the payment.

Returns​

PromisePromise<PaymentProcessorError | PaymentProcessorSessionResponse>Required
Either the payment's data or an error object.

deletePayment​

This method is used to perform any actions necessary before a Payment Session is deleted. The Payment Session is deleted in one of the following cases:

  1. When a request is sent to delete the Payment Session.
  2. When the Payment Session is refreshed. The Payment Session is deleted so that a newer one is initialized instead.
  3. When the Payment Processor is no longer available. This generally happens when the store operator removes it from the available Payment Processor in the admin.
  4. When the region of the store is changed based on the cart information and the Payment Processor is not available in the new region.

Example​

import {
  PaymentProcessorError,
  // ...
} from "@medusajs/medusa"
// ...

class MyPaymentService extends AbstractPaymentProcessor {
  // ...
  async deletePayment(
    paymentSessionData: Record<string, unknown>
  ): Promise<Record<string, unknown> | PaymentProcessorError> {
    const paymentId = paymentSessionData.id
    // assuming client is an initialized client
    // communicating with a third-party service.
    this.client.delete(paymentId)

    return {}
  }
}

Parameters​

paymentSessionDataRecord<string, unknown>Required
The data field of the Payment Session.

Returns​

PromisePromise<Record<string, unknown> | PaymentProcessorError>Required
Either an error object or an empty object.

getPaymentStatus​

This method is used to get the status of a Payment or a Payment Session. Its main usage is within the place order and create swap flows. If the status returned is not authorized within these flows, then the payment is considered failed and an error will be thrown, stopping the flow from completion.

Example​

import {
  PaymentSessionStatus
  // ...
} from "@medusajs/medusa"
// ...

class MyPaymentService extends AbstractPaymentProcessor {
  // ...
  async getPaymentStatus(
    paymentSessionData: Record<string, unknown>
  ): Promise<PaymentSessionStatus> {
    const paymentId = paymentSessionData.id

    // assuming client is an initialized client
    // communicating with a third-party service.
    return await this.client.getStatus(paymentId) as PaymentSessionStatus
  }
}

Parameters​

paymentSessionDataRecord<string, unknown>Required
The data field of a Payment as a parameter. You can use this data to interact with the third-party provider to check the status of the payment if necessary.

Returns​

PromisePromise<PaymentSessionStatus>Required
The status of the Payment or Payment Session.

refundPayment​

This method is used to refund an order’s payment. This is typically triggered manually by the store operator from the admin. The refund amount might be the total order amount or part of it.

This method is also used for refunding payments of a swap or a claim of an order, or when a request is sent to the Refund Payment API Route.

You can utilize this method to interact with the third-party provider and perform any actions necessary to refund the payment.

Example​

import {
  PaymentProcessorError,
  // ...
} from "@medusajs/medusa"
// ...

class MyPaymentService extends AbstractPaymentProcessor {
  // ...
  async refundPayment(
    paymentSessionData: Record<string, unknown>,
    refundAmount: number
  ): Promise<Record<string, unknown> | PaymentProcessorError> {
    const paymentId = paymentSessionData.id

    // assuming client is an initialized client
    // communicating with a third-party service.
    const refundData = this.client.refund(paymentId, refundAmount)

    return {
      id: paymentId,
      ...refundData
    }
  }
}

Parameters​

paymentSessionDataRecord<string, unknown>Required
The data field of a Payment.
refundAmountnumberRequired
the amount to refund.

Returns​

PromisePromise<Record<string, unknown> | PaymentProcessorError>Required
Either an error object or a value that's stored in the data field of the Payment.

retrievePayment​

This method is used to provide a uniform way of retrieving the payment information from the third-party provider. For example, in Stripe’s Payment Processor this method is used to retrieve the payment intent details from Stripe.

Example​

import {
  PaymentProcessorError
  // ...
} from "@medusajs/medusa"
// ...

class MyPaymentService extends AbstractPaymentProcessor {
  // ...
  async retrievePayment(
    paymentSessionData: Record<string, unknown>
  ): Promise<Record<string, unknown> | PaymentProcessorError> {
    const paymentId = paymentSessionData.id

    // assuming client is an initialized client
    // communicating with a third-party service.
    return await this.client.retrieve(paymentId)
  }
}

Parameters​

paymentSessionDataRecord<string, unknown>Required
The data field of a Payment Session. Make sure to store in the data field any necessary data that would allow you to retrieve the payment data from the third-party provider.

Returns​

PromisePromise<Record<string, unknown> | PaymentProcessorError>Required
The payment's data, typically retrieved from a third-party provider.

updatePayment​

This method is used to update the payment session when the payment amount changes. It's called whenever the cart or any of its related data is updated. For example, when a line item is added to the cart or when a shipping method is selected.

Example​

import {
  PaymentProcessorContext,
  PaymentProcessorError,
  PaymentProcessorSessionResponse,
  // ...
} from "@medusajs/medusa"
// ...

class MyPaymentService extends AbstractPaymentProcessor {
  // ...
  async updatePayment(
    context: PaymentProcessorContext
  ): Promise<
    void |
    PaymentProcessorError |
    PaymentProcessorSessionResponse
  > {
    // assuming client is an initialized client
    // communicating with a third-party service.
    const paymentId = context.paymentSessionData.id

    await this.client.update(paymentId, context)

    return {
      session_data: context.paymentSessionData
    }
  }
}

Parameters​

contextPaymentProcessorContextRequired
The context of the payment.

Returns​

PromisePromise<void | PaymentProcessorError | PaymentProcessorSessionResponse>Required
Either the payment's data or an error object.

updatePaymentData​

This method is used to update the data field of a payment session. It's called when a request is sent to the Update Payment Session API Route, or when the CartService's updatePaymentSession is used.

This method can also be used to update the data in the third-party payment provider, if necessary.

Example​

import {
  PaymentProcessorError,
  PaymentProviderService,
  // ...
} from "@medusajs/medusa"
// ...

class MyPaymentService extends AbstractPaymentProcessor {
  protected paymentProviderService: PaymentProviderService
  // ...
  constructor(container, options) {
    super(container)
    this.paymentProviderService = container.paymentProviderService
    // ...
  }
  // ...
  async updatePaymentData(
    sessionId: string,
    data: Record<string, unknown>
  ): Promise<
    Record<string, unknown> |
    PaymentProcessorError
  > {
    const paymentSession = await this.paymentProviderService.retrieveSession(sessionId)
    // assuming client is an initialized client
    // communicating with a third-party service.
    const clientPayment = await this.client.update(paymentSession.data.id, data)

    return {
      id: clientPayment.id
    }
  }
}

Parameters​

sessionIdstringRequired
The ID of the payment session.
dataRecord<string, unknown>Required
The data to be updated in the payment session.

Returns​

PromisePromise<Record<string, unknown> | PaymentProcessorError>Required
the data to store in the data field of the payment session. You can keep the data as-is, or make changes to it by communicating with the third-party provider.

Test Implementation​

Note

If you created your payment processor in a plugin, refer to this guide on how to test plugins.

After finishing your payment processor implementation:

1. Run the build command in the root of your Medusa backend:

npm run build

2. Start the backend with the develop command:

npx medusa develop

3. Enable your payment processor in one or more regions. You can do that either using the Admin APIs or the Medusa Admin.

4. There are different ways to test out your payment processor, such as authorizing payment on order completion or capturing payment of an order. You test payment in a checkout flow either using the Next.js starter or using Medusa's APIs and clients.

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