We can hide the theme's default add-to-cart button if you prefer to add your own custom code or 3rd party app to the cart. Follow these steps to do this:
STEP 1
From your Shopify admin, navigate to the Theme library and open your theme customizer.
STEP 2
Go to Theme Settings, click Custom Script/Style, and paste this code:
.btn--primary.btn--add-to-cart{
display:none;
}
STEP 3
Don't forget to apply the changes.