Why is 'Shipping not available for selected address' showing at checkout?

[Reims]

Hi there,

When someone tried to checkout of my store, it says "Shipping not available for selected address." I have my shipping settings linked to my supplier app (DSers) and it's listed as shipping to "rest of world." Now in the midst of trying to fix this for the last couple of days, my product prices have changed on my customer website but not on my product page or in customer checkout.... Does anybody have any advice? 

Anything would be much appreciated

Thanks