You need to provide the domain for your application, which varies based on your application’s type and marketplace.
For Public Applications & Private Seller Applications (authorized through Seller Central),you should use the Seller Central domain.
For Private Vendor Applications (authorized through Vendor Central), you should use the Vendor Central domain.
To find the correct domain for your marketplace, visit this link.
For example, based on the table, the Seller Central URL for the Saudi Arabia marketplace is https://sellercentral.amazon.com.sa, so the full domain is sellercentral.amazon.com.sa.
Please visit this link to find the proxy base URL for your API endpoint. For example, for the North America selling region (including Canada, US, Mexico, and Brazil marketplaces), the endpoint is https://sellingpartnerapi-na.amazon.com, and the proxy baseUrl region will be na.