I tried to get a straight answer from the support but they kept on telling me that I could just put my customized domain as the primary domain, which is not true.
So is there a way to replace the shop.myshopify.com domain in the checkout on a lite plan in 2020? Or is it only available to Shopify Plus plans?
Elias here with Shopify Support. Thanks for reaching out.
I can confirm that changing your primary domain to your custom domain, will replace the checkout URL with your custom domain. This change was introduced back in July of 2017 and you can find it on our changelogs or announcement pages. However, it's important to note, this isn't available on the Shopify Lite plan. This is because the Shopify Lite plan doesn't have an Online store, so you won't be able to connect a custom domain.
That being said, this isn't exclusive to Shopify Plus. It's available on any of our plans (eg. Shopify Basic, Shopify, Shopify Advanced) - as long as you have an Online store.
I hope this helps clarify the checkout domains. If you have any other questions on this topic, don't hesitate to let me know!