Welcome to the Shopify Community, and thanks for sharing your question!
I understand that your customers are unable to complete their purchase on your store. You also mentioned you're unable to pay for product(s) as well.
Are you able to share a bit more context in regard to the issue? I'll share a few points below to better help identify the issue:
What payment gateway is this occurring on?
Are there any error messages in your Settings > Payments section of your Shopify admin?
What is the specific error message or issue when attempting to make a payment?
Could you share a link to your store, as well as a screenshot of the error?
If you're able to ensure that your payment gateway is set up correctly and activated. You can also check that you have entered the correct credentials and that the payment gateway supports the customer's chosen payment method.
I'm looking forward to your reply and learning more.
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