Need Someone Who Can Direct All My Product Listing To Checkout.domain.com

Hi, I have a website called fernqdesigns.com. When I add to cart the featured product in the home page and click on checkout, it goes to checkout.fernqdesigns.com But when I choose other products to add to cart and click on checkout button. It goes to this URL https://fernqdesigns.com/checkouts/ I'm using Shrine Theme Lite. The custom checkout domain is used by my customer payment called Tagada.io I hope someone can help me out. Looking forward to hearing from you. Regards, Cyrus Sandoval