Can't obtain access token via API

Hello!

I want to upload files via API, but I'm stuck at the access token.

I already went to control panel -> API settings, enabled it and added an API client where I got my client ID and Secret.

I'm trying to make a post call to myserver.com/oauth2/authorize as mentioned in the documentation, with the following parameters:

client_id (the client ID I got in the control panel)
scope email profile (as in the documentation example)
redirect_url otherserver.com/some/handler.php (this URL is in the authorized list)
response_type code
state SOMERANDOMTEXT

I do get response from the server, but that response is the HTML from the login page, I was expecting an access token...

What I'm I missing????

PS: Attached screenshot, only values marked in pink are being used in this example.

Error Screen