Tira here, from Shopify Support.
Welcome to Shopify! I am happy to help you here and would like to ask some questions to assist you with your inquiry.
It sounds like you're trying to set-up a payment gateway on your store. We have a collection of help docs that you can check out to learn more about setting up payments on your store, here: Payment Methods. What payment provider are you using on your store?
If you could let me know what that is, I can provide more guidance or resources. I look forward to hearing from you.