In POS extensions, it possible to block checkout conditionally?
There is a useBuyerJourney api in checkout ui extension. But seems not available in POS.
Is is possible to do that? And if not, does Shopify has plan to implement this feature?
My use case is that we have a checkout ui extension on our online shop that will calculate customer’s purchase quota.
If our customer checkout exceed the quota we define, we will block their checkout.
We want to implement similar thing in POS.
Thanks 
At this time no - you cannot intercept or alter the purchasing journey in the POS yet.
I’ve heard that similar extension endpoints are coming to the POS system. Which would be great.
But I believe at this time you’re limited to post-purchase actions and adding tiles to the home screen.
If this has changed, I would love to know. I’ve tracking this as well.
Hope that we will hear good news from Shopify soon.
Currently we are relying on cashier staff to open the tile in home screen to check whether customer exceed the quota. And it is time-consuming and error-prone if we rely that on human effot 
I definitely understand that @Tom_Chan , we’re in a similar situation. Merchants want to be able to block an in-progress transaction or at least prompt for an action depending on the products in the cart, etc.
So a similar pattern to the buyerJourneyIntercept available in the Checkout UI Extensions + a new in-cart mount point would be perfect.
We just have to stay tuned to the POS Extensions Changelog and hope something is released that solves this gap.