As per the below link and description
https://shopify.dev/apps/payments/processing-a-payment#retry-policy.
Below documentation is saying that we need to inform customer that that the payment is processed, but Shopify is unreachable. You can let the customer know that they will receive a notification from Shopify when the order is processed during retry. the response from shopify contains redirection URL after retry is successful. what is the behavior and should we still redirect customer to redirect URL and what if customer closes the browser after he receive notification from payment about the error.
If there’s a Shopify service disruption (or if 5xx status codes are being returned), then requests must be retried. It’s suggested to follow the guidelines in the retry policy section.
If a GraphQL request acknowledgment is not received, then you need to implement a retry policy. During this time, you can inform the customer that the payment is processed, but Shopify is unreachable. You can let the customer know that they will receive a notification from Shopify when the order is processed. Furthermore, the customer should contact the merchant directly if the maximum number of recommended retries elapses without acknowledgment.