I also am having trouble with the express in checkout. It tells me, "express checkout isn't available right now. Try refreshing the page or fill out your information to check out."
I went to Shopify Payments, and set up my paypal business account, and it tells me its all connected.
I went back to the checkout, and it still says what it says above, That express checkout isnt available right now. Is there something else I need to do?