This is because your IIS doesn’t have json MIME Type.
Open IIS Manager -> Mime types -> Add a new mime type like below
Extension: .json MIME Type: application/json
OR
Insert mimeMap like below in web.config.
<system.webServer>
<staticContent>
<mimeMap fileExtension=".json" mimeType="application/json" />
</staticContent>
</system.webServer>