Why can't I generate user token in Instagram API?

I'm trying to use instagram api to show #'s on my webpage but i need to generate user token for instagram tester. I followed the documentatio (created an application, use my page url, sent invitation for instagram tester and accepted it) but when i click on generate token for instagram tester it displays a pop-up window to allow permissions, then it shows nothing. I tried with another account, creating a different application but the result is the same.

Facebook token generator seems to be broken, but you can generate your own long-lived access token following OAuth2 workflow (replace {} placeholders with your own values):

1. In your browser, go to:

https://api.instagram.com/oauth/authorize?client_id={your-client-id}&client_secret={your-client-secret}&redirect_uri={a-valid-redirect-url}&scope=user_profile,user_media&response_type=code

2. Login to your Instagram account and accept your application to access your data
3. You should be redirected to {a-valid-redirect-url}?code=xxxxx#_ then copy to {code} query string value without the #_ at the end
4. Use Postman to execute a POST request to https://api.instagram.com/oauth/access_token with x-www-form-urlencoded params
   • client_id: {your-client-id}
   • client_secret: {your-client-secret}
   • grant_type: authorization_code
   • redirect_uri: {a-valid-redirect-url}
   • code: {the code you extracted from query string}
5. You should get a short-lived access-token response such as:

{
    "access_token": "IGQVxxxxxxxxxx…",
    "user_id": xxxxxxxxxx
}

6. Exchange your short-lived access-token with a long-lived one: use Postman to execute a GET request to https://graph.instagram.com/access_token with query params:
   • client_id: {your-client-id}
   • client_secret: {your-client-secret}
   • grant_type: ig_exchange_token
   • access_token: {the short-lived access_token}
7. You should get a long-lived access-token response such as:

{
    "access_token": "IGQxxxxx…",
    "token_type": "bearer",
    "expires_in": 5169852
}