I suspect that the shipping zone settings on your Shopify store might have something to do with this.
Head to Settings > Shippings & Delivery and check if all the countries you deliver to are configured here. There should be an option to set that you can ship anywhere in the world too.
You can check out this blog for step by step info on how to do this.
Let me know if this solved the problem you were facing.
In the same settings, there should be an option to set shipping rates based on zones.
Do check if your shipping rates are set there. If they are, ideally they should reflect on your store when someone is trying to purchase from that zone.
Unfortunately, the only thing that shows up in the shipping settings for manage rates is this: USPS (Discounted rates from Shopify Shipping), which I know nothing about. There should be USPS International that is based on where it's being shipped to, but that option is nowhere to be found. What's frustrating is that if I could speak with someone at shopify, it could probably be taken care of in a few minutes. I see no need for such complex issues in setting this up. So this just goes on and on.