Why can't customers purchase from my US-based online store?

So basically i´m selling in the US but i´m living in Germany.

I thought that everything is working out fine but now I received a message that a customer could not order.

I can´t find the problem because I can´t test what problems occur during the checkout process.

Can someone tell me what the problem might be?

I´m having my first 300 visitors but no one seems to buy and after that message i just need to fix that problem as fast as possible!

https://kingmobileshop.com/products/airpod-cleaner

Hi @Adrik501 ,

You can test the payments by following the instructions here. https://help.shopify.com/en/manual/payments/shopify-payments/testing-shopify-payments

Okay, so the customer stated that his credit card is getting declined. Although everything is fine on his side so i don´t get it…