To gather a bit more context, could you share more information on the following:
Which payment gateway are customers attempting to use when checking out?
Are there any additional error messages in the abandoned checkout section? This can be located within your Shopify admin under Products > Abandoned checkouts. You can view the order timeline of the affected abandoned checkout.
Can you share a screenshot of the error message at checkout?
In the meantime, could you ensure that your store is not in test mode? While test mode is activated, you can't use real credit cards to pay for orders. If test mode is enabled, you can deactivate it so that your customers can pay for their orders using their real credit cards. I'll share our Testing Shopify Payments resource for more information.
I look forward to hearing back and learning more.
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