Unable to Publish Offer via Inventory API – Item.Country Error and merchantLocationKey Not Available

[japanbaitstore]

Hello,
I am trying to publish a listing via Inventory API.

- Inventory item creation: ✅ Success
- Offer creation: ✅ Success
- Publish: ❌ Fails with error: "No <Item.Country> exists or <Item.Country> is specified as an empty tag"

I also tried using "merchantLocationKey": "default" in both inventory and offer calls, but I get:

"Location information not found"

Even the POST /location endpoint fails with "Invalid request" (400), so I cannot create an inventory location.

Thanks in advance.