Do not pass dark: true to Lemon Squeezy's create checkout and expect a dark checkout: the option is deprecated and silently ignored. Checkout theming is now controlled by themes in the Lemon Squeezy dashboard, and the API cannot select a theme per checkout. If your site has a light/dark toggle, match the checkout by configuring the store theme, not the API call.

Context: GitHub issue lmsqueezy/lemonsqueezy.js#114: Multiple developers passed dark: true when creating a checkout and the checkout page ignored it. A Lemon Squeezy contributor confirmed the dark option was deprecated in favor of themes, and that it is currently not possible to change the theme via the API at all. The docs and SDK were updated to remove the option.