How to work with Shopify checkout UI extension?

[Zaven93]

Hi there guys, is there anybody who worked with Shopify checkout UI extension, not post-purchase one. For me, it's very surprising why the Shopify team released the documentation on how to create a post-purchase extension but haven't regarding the checkout UI extension. Any suggestions are welcomed. 
Best regards!

[agustin-lavalla]

Any update on this? I'm trying to add a checkout UI extension but it is not reflected on the checkout. Has anyone been able to implement the extensions?