Cannot create SinchClient instance

Question

I have a problem with SInchClient. Everytime I instantiate a new instance of SinchClient, I get this error:

Response { type: "cors", url: "https://ocra.api.sinch.com/ocra/v2/applications/.../instances", redirected: false, status: 400, ok: false, statusText: "Bad Request", headers: Headers(2), body: ReadableStream, bodyUsed: false }
​
body: ReadableStream { locked: false }
​
bodyUsed: false
​
headers: Headers { "content-length" → "211", "content-type" → "application/json" }
​
ok: false
​
redirected: false
​
status: 400
​
statusText: "Bad Request"
​
type: "cors"
​
url: "https://ocra.api.sinch.com/ocra/v2/applications/..../instances"
​
<prototype>: ResponsePrototype { clone: clone(), arrayBuffer: arrayBuffer(), blob: blob(), … }
sinch-rtc-min.js:2:460086

{
      "message": "Unable to create instance!",
      "code": 500,
      "domain": 2
}

I followed this tutorial: Getting started with Sinch In-app Calling for JavaScript SDK

I also test this samples on my machine and got the same error. Is there a way to fix this? Also, follow-up question. How to call an app in browser using a phone? In the samples above, there's only browser-to-phone call sample.