The customer cannot check out.
WHAT IT MEANS
No shipping zone covers the customer's address, so nothing can be offered.
THE FIX
WooCommerce > Settings > Shipping. Confirm a zone covers that region, and that the zone has at least one method with a rate.
A zone with no method configured produces exactly this.
THE ORDER OF ZONES
Zones are matched top down, and the first match applies. A general zone above a specific one prevents the specific one ever being used.
Put specific zones first.
THE CATCH-ALL
Create a zone covering everywhere else, at the bottom. Either give it a rate, or a method that states you do not deliver there.
Without it, any address outside your defined zones cannot check out at all.
FOR DIGITAL PRODUCTS
Mark them virtual and downloadable. WooCommerce then skips shipping entirely.
A single non-virtual product in the cart reinstates the shipping requirement for the whole order.
TESTING
Add a product and enter addresses in each region you serve, plus one you do not. Confirm the right outcome each time.