Our Share the Love app works by passing cart note attributes directly from the cart page to the Shopify Checkout. This means that the customer will have to click a checkout button that has our application present within the same form tag.
The Buy Now buttons bypass the cart entirely, and are incapable of passing cart note attributes. This is an issue which has been brought up by many app developers, and unfortunately has not been resolved, and likely will not be due to the nature of the Buy Now buttons.
This unfortunately means that if a customer uses a Buy Now button to reach the checkout page, then our application will be completely bypassed, and will not allow the customer to select a cause to donate to, and the donation will show up as "Error: None Selected" within our app.
Here is a brief article by Shopify outlining this issue:
Unfortunately, this app is not compatible with buy now or dynamic checkout buttons. Nor is any app in the Shopify app market which offers similar functionality to ours. The buy now/dynamic checkout buttons are inherently flawed, in that they do not offer any solutions for third-party applications to work in conjunction with them.