That error means either that you've misconfigured the app or that the authentication call is incorrect.

Note that stackexchange.com/oauth/login_success is not a valid redirect_uri irregardless.

You probably want/need to use Client side (Implicit) authentication, in which case the redirect_uri would be:

          https://stackexchange.com/oauth/login_success

Note the mandatory https://.

Be sure your app is configured as shown in this answer.

Then you can use a URL like the following to authenticate:

https://stackexchange.com/oauth/dialog?client_id={YOUR CLIENT ID}&scope=no_expiry&redirect_uri=https://stackexchange.com/oauth/login_success

When you fetch that page, something like this will end up as the redirected-to URL:

https://stackexchange.com/oauth/login_success#access_token=wdR8Lm7m4ibD48lfrCcFxQ))&expires=86399

You would then use the access_token to make an API query like:

https://api.stackexchange.com/2.2/questions/30028657/answers?site=stackoverflow&key=RoZwtHUrhMP088oVGCMlxA((&access_token=wdR8Lm7m4ibD48lfrCcFxQ))&filter=!)4k-FmUi-xgG3sdSdPz*cQNNqR0A

(Note that the example token, above, has long since been invalidated. Use your own values for it and for key.)

That error means either that you've misconfigured the app or that the authentication call is incorrect.

Note that stackexchange.com/oauth/login_success is not a valid redirect_uri irregardless.

You probably want/need to use Client side (Implicit) authentication, in which case the redirect_uri would be:

          https://stackexchange.com/oauth/login_success

Note the mandatory https://.

Be sure your app is configured as shown in this answer.

Then you can use a URL like the following to authenticate:

https://stackexchange.com/oauth/dialog?client_id={YOUR CLIENT ID}&scope=no_expiry&redirect_uri=https://stackexchange.com/oauth/login_success

When you fetch that page, something like this will end up as the redirected-to URL:

https://stackexchange.com/oauth/login_success#access_token=wdR8Lm7m4ibD48lfrCcFxQ))&expires=86399

You would then use the access_token to make an API query like:

https://api.stackexchange.com/2.2/questions/30028657/answers?site=stackoverflow&key=RoZwtHUrhMP088oVGCMlxA((&access_token=wdR8Lm7m4ibD48lfrCcFxQ))&filter=!)4k-FmUi-xgG3sdSdPz*cQNNqR0A

(Note that the example token, above, has long since been invalidated. Use your own values for it and for key.)