In order to retry the payment, you should go to "Orders" tab in your Printify account.
There you will be able to locate the order with the status “Payment Not Received.”
Clicking the “Retry” button will retry the billing process and the order will be sent to production as soon as the payment has been received.
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If retrying the payment is still unsuccessful then the issue is likely with your payment method and you may need to provide an alternate credit/debit card or contact your bank to determine why the payment is being declined.