With Checkout Page, you can easily create a one page checkout and add it to your site in different ways.

Here are the instructions for Mailchimp.

Add a Buy button

1. Open the Site Builder on Mailchimp
2. Click on any button in your layout or add a new section including a button
3. From the button menu, select the first icon to add a link
4. Open your Checkout Page dashboard, click on the checkout you'd like to link to and then Add to site
5. Copy the Payment link
6. Back on Mailchimp, paste this link into the URL field and save

7. Double-click on the button text to edit it 8. Click Done to save and Publish your page

At this time, Mailchimp users can only add a Buy button linking to your checkout on Checkout Page.

Mailchimp does not support any custom HTML needed for your checkout pop-up or embed.