Merchant Id when processing a payment using payment app

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1

Hello,

When processing a payment with Shopify payment app the first step is for Shopify to make a POST request to payment application to initiate the payment. The request body is documented in this section https://shopify.dev/apps/payments/processing-a-payment#how-a-payment-flow-works

  1. The request body does not contain any information on the merchant for which this payment needs to be processed. How would the payment application know which merchant account to use. ?
  2. Does Shopify use an access token when calling the payment session URL ? If not then does this URL need to be a publicly available URL ?

Thank you in advance for your help.

2

You should check out the headers on the request - specifically shopify-shop-domain for determining the relevant merchant